WinForms and Android refactor for Container

[johnzhou721]

Container and Windowss on Winforms and Android now uses a "has-a" relationship instead of a "is-a" relationship. This will simplify scaffold implementation later, as there's an additioanl layer that manages containers.

Refs #4382.

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

Assisted-by:

[kattni]

@johnzhou721 Please merge main into this PR. The docs failure is due to an update that isn't currently included here.

Tag me when you've done so. Thank you.

[johnzhou721]

@kattni I've merged with main; thanks.

[phildini]

This seems reasonable; is it truly the case that no tests are needed here?

[johnzhou721]

@phildini

This seems reasonable; is it truly the case that no tests are needed here?

First off, thank you for taking the time to review this pull request and suggest the addition of new tests.

I believe that there should not be a need for additional tests, as these are merely changes in the internal structure of how Window is handled, rather than new behaviors; existing behaviors related to Container would all be covered in existing tests.

If there is anything else you would like to see tested, please let me know so I can add them.

[kattni]

Thank you for following up. One minor change applied.

[kattni]

setuptools_scm had a dependency update that required it be updated for compatibility. Update pushed.

[freakboy3742]

The setuptools_scm issues turned into a bigger problem; see #4498 for the updates required.

[johnzhou721]

@kattni I'm seeing merge conflicts here; unfortunately I do not have an idea of the additional changes that has been pushed to this PR. If I understand, anything after de02db0 has been moved to #4498. Is that correct? If so, I'll hard reset to de02db0 and then force push here.

[kattni]

@johnzhou721 I've merged main and pushed. Letting CI run now.