[7.x] Use embeddable v2 (#39126)

[stacey-gammon]

backports #39126

• Final Embeddable API V2 PR

• fix: import discover embeddable scss file

• address code review comments

• Add a functional test that would have caught the bug... will look to add a unit version once I discover the error.

• Fix bug cause by async loading calls and changes to parent input while child is being created. added jest test

• remove outdated readme in dashboard folder

• need to always refresh dashboard container, not just when "dirty"

• add a wait, this issue started appearing right when I added this to the test

• Remove test that kills kibana ci so it's not a blocker. jest test was added for this scenario

• fix issues when panel is added then removed before it completes loading

• fix logic error with maps embeddable and isLayerTOCOpen

Summary

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Checklist

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• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request