form elements: add AttachInternals

[QuintonJason]

Description

There is a need coming from XF to expose the ElementInternals interface to our web components. The ElementInternals interface of the DOM gives web developers a way to allow custom elements to fully participate in HTML forms.

Type of change

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• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

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• unit tests
• e2e tests
• accessibility tests
• tested manually
• other:

Test Configuration:

• Pine versions:
• OS:
• Browsers:
• Screen readers:
• Misc:

Checklist:

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• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Design has QA'ed and approved this PR

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