date knob incorrectly deserializes value

[cellog]

Describe the bug
https://github.com/storybookjs/storybook/blob/next/addons/knobs/src/converters.ts#L18 has this deserialization code:

 (value: any): number => new Date(value).getTime() || new Date().getTime(),

However, since value is a Date when used in the iframe, but is a number when used in a new tab (by clicking on the open Canvas in new tab button), it always initializes to the current date.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/Date

When deserializing, the value is a string instead of a number, and so will be the string representation of the timestamp. The Date object then tries to parse this string as a date string, fails, and falls back to today's date.

fix is straightforward:

 (value: string | number): number => new Date(+value).getTime() || new Date().getTime(),

To Reproduce
Steps to reproduce the behavior:

1. add a date knob
2. set a value
3. open the canvas in a new tab

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Code snippets
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System
Please paste the results of npx sb@next info here.

Additional context
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[shilman]

FYI, we’ve released addon-controls in Storybook 6.0. Controls are portable, auto-generated knobs that are intended to replace addon-knobs, which are slated for deprecation.

• Controls documentation
• Migration instructions

Please upgrade and try out controls today!

[cellog]

thanks, we are aware of controls. We also have a gigantic codebase, so the migration has not happened yet.