Rust: Remove elements superseded by attribute macro expansions

[hvitved]

Follows up on #20454 and removes elements superseded by attribute macro expansions entirely from the Element type. We only ever care about the expanded version, which will typically contain a copy of the original definition.

DCA looks good: we reduce inconsistencies, increase call resolution rates, and eliminate rust/unused-variable false positives.

[Copilot]

Pull Request Overview

This PR refactors macro expansion handling in the Rust QL library by consolidating logic into a central MacroExpansion module and introducing the isFromMacroExpansion() predicate to better distinguish between macro arguments and macro-generated code. The changes improve code organization, reduce duplication, and update test expectations to reflect the new behavior.

• Centralized macro expansion logic from MacroCallImpl and PathResolution into ElementImpl::MacroExpansion
• Introduced isFromMacroExpansion() to exclude macro arguments from expansion checks
• Updated queries to use the new predicate where appropriate
• Added custom toString() for items with attribute macro expansions

Reviewed Changes

Copilot reviewed 25 out of 25 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/elements/internal/ElementImpl.qll	Adds centralized MacroExpansion module with logic for classifying macro-related elements
rust/ql/lib/codeql/rust/elements/internal/AstNodeImpl.qll	Updates isInMacroExpansion() and isFromMacroExpansion() to delegate to MacroExpansion module
rust/ql/lib/codeql/rust/elements/internal/MacroCallImpl.qll	Removes isInMacroExpansion() and getATokenTreeNode() logic, now in ElementImpl
rust/ql/lib/codeql/rust/elements/internal/ItemImpl.qll	Adds custom toString() for items with attribute macro expansions
rust/ql/lib/codeql/rust/elements/internal/LocatableImpl.qll	Updates to use new getImmediatelyEnclosingMacroInvocation() helper
rust/ql/lib/codeql/rust/internal/PathResolution.qll	Simplifies ItemNode constructor by removing supersededByAttributeMacroExpansion()
rust/ql/src/queries/unusedentities/UnusedValue.ql	Updates to use isFromMacroExpansion() instead of isInMacroExpansion()
rust/ql/src/queries/unusedentities/UnreachableCode.ql	Updates to use isFromMacroExpansion() instead of isInMacroExpansion()
rust/ql/src/queries/unusedentities/UnusedVariable.qll	Adds TODO comment noting future migration to isFromMacroExpansion()
rust/ql/lib/utils/test/PathResolutionInlineExpectationsTest.qll	Simplifies itemAt() by removing unused inMacro parameter
rust/ql/test/library-tests/variables/variables.ql	Updates to use isFromMacroExpansion() instead of isInMacroExpansion()
Test expectation files	Updates expected test outputs to reflect deduplication and new behavior
.gitattributes and .generated.list	Removes ItemImpl.qll from generated file list

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