[material_ui] Migrate M3 buttons template to use new gen_defaults

[QuncCccccc]

Work towards flutter/flutter#187899

Fixes flutter/flutter#188405

Pre-Review Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools.
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• I read and followed the [relevant style guides] and ran [the auto-formatter].
• I signed the [CLA].
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I [linked to at least one issue that this PR fixes] in the description above.
• I followed [the version and CHANGELOG instructions], using [semantic versioning] and the [repository CHANGELOG style], or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which [test exemption] this PR falls under[^1].
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request migrates Material 3 button defaults to be generated from tokens via a new ButtonTemplateM3 template, removing hardcoded default classes from the button implementation files and generating them as part files instead. The review feedback suggests modernizing the generated code by replacing deprecated MaterialStatePropertyAll references with WidgetStatePropertyAll in both the template and its associated tests.

[gemini-code-assist]

Since this is a new template migration, we should use the modern WidgetStatePropertyAll instead of the legacy/deprecated MaterialStatePropertyAll to align with Flutter's ongoing migration from MaterialState to WidgetState.

Suggested change

	String get _backgroundColor {
	final TokenColorRole? containerColor = _containerColor;
	if (containerColor == null) {
	return 'const MaterialStatePropertyAll<Color>(Colors.transparent)';
	}
	String get _backgroundColor {
	final TokenColorRole? containerColor = _containerColor;
	if (containerColor == null) {
	return 'const WidgetStatePropertyAll<Color>(Colors.transparent)';
	}

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for consistency and modernization.

Suggested change

	String get _shadowColor {
	return switch (_variant) {
	_ButtonVariant.elevated =>
	'MaterialStatePropertyAll<Color>(${color(TokenButtonElevated.containerShadowColor, '_colors')})',
	_ButtonVariant.filled =>
	'MaterialStatePropertyAll<Color>(${color(TokenButtonFilled.containerShadowColor, '_colors')})',
	_ButtonVariant.filledTonal =>
	'MaterialStatePropertyAll<Color>(${color(TokenButtonTonal.containerShadowColor, '_colors')})',
	_ButtonVariant.outlined ||
	_ButtonVariant.text => 'const MaterialStatePropertyAll<Color>(Colors.transparent)',
	};
	}
	String get _shadowColor {
	return switch (_variant) {
	_ButtonVariant.elevated =>
	'WidgetStatePropertyAll<Color>(${color(TokenButtonElevated.containerShadowColor, '_colors')})',
	_ButtonVariant.filled =>
	'WidgetStatePropertyAll<Color>(${color(TokenButtonFilled.containerShadowColor, '_colors')})',
	_ButtonVariant.filledTonal =>
	'WidgetStatePropertyAll<Color>(${color(TokenButtonTonal.containerShadowColor, '_colors')})',
	_ButtonVariant.outlined ||
	_ButtonVariant.text => 'const WidgetStatePropertyAll<Color>(Colors.transparent)',
	};
	}

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for the outlined and text button elevation defaults.

Suggested change

	String get _elevation {
	if (_variant == _ButtonVariant.outlined || _variant == _ButtonVariant.text) {
	return 'const MaterialStatePropertyAll<double>(0.0)';
	}
	String get _elevation {
	if (_variant == _ButtonVariant.outlined || _variant == _ButtonVariant.text) {
	return 'const WidgetStatePropertyAll<double>(0.0)';
	}

[gemini-code-assist]

Use WidgetStatePropertyAll to match the WidgetStateProperty return type.

Suggested change

	@override
	WidgetStateProperty<TextStyle?> get textStyle =>
	MaterialStatePropertyAll<TextStyle?>($_buttonTextStyle);
	@override
	WidgetStateProperty<TextStyle?> get textStyle =>
	WidgetStatePropertyAll<TextStyle?>($_buttonTextStyle);

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for surfaceTintColor.

Suggested change

	@override
	WidgetStateProperty<Color>? get surfaceTintColor =>
	const MaterialStatePropertyAll<Color>(Colors.transparent);
	@override
	WidgetStateProperty<Color>? get surfaceTintColor =>
	const WidgetStatePropertyAll<Color>(Colors.transparent);

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for minimumSize.

Suggested change

	@override
	WidgetStateProperty<Size>? get minimumSize =>
	const MaterialStatePropertyAll<Size>(Size(64.0, ${number(TokenButton.containerHeight)}));
	@override
	WidgetStateProperty<Size>? get minimumSize =>
	const WidgetStatePropertyAll<Size>(Size(64.0, ${number(TokenButton.containerHeight)}));

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for iconSize.

Suggested change

	@override
	WidgetStateProperty<double>? get iconSize => const MaterialStatePropertyAll<double>($_legacyIconSize);
	@override
	WidgetStateProperty<double>? get iconSize => const WidgetStatePropertyAll<double>($_legacyIconSize);

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for maximumSize.

Suggested change

	@override
	WidgetStateProperty<Size>? get maximumSize => const MaterialStatePropertyAll<Size>(Size.infinite);
	@override
	WidgetStateProperty<Size>? get maximumSize => const WidgetStatePropertyAll<Size>(Size.infinite);

[gemini-code-assist]

Use WidgetStatePropertyAll instead of MaterialStatePropertyAll for shape.

Suggested change

	@override
	WidgetStateProperty<OutlinedBorder>? get shape =>
	const MaterialStatePropertyAll<OutlinedBorder>(${shape(TokenButton.containerShapeRound, '')});
	@override
	WidgetStateProperty<OutlinedBorder>? get shape =>
	const WidgetStatePropertyAll<OutlinedBorder>(${shape(TokenButton.containerShapeRound, '')});

[gemini-code-assist]

Update the test expectation to expect WidgetStatePropertyAll instead of MaterialStatePropertyAll to match the updated template.

Suggested change

	expect(
	contents,
	contains('MaterialStatePropertyAll<TextStyle?>(Theme.of(context).textTheme.labelLarge)'),
	);
	expect(
	contents,
	contains('WidgetStatePropertyAll<TextStyle?>(Theme.of(context).textTheme.labelLarge)'),
	);