[select] fix: use renderTarget API to fix fill prop

[adidahiya]

Fixes #5353

Checklist

• Includes tests - covered by existing test suite
• Update documentation

Changes proposed in this pull request:

Select2, Suggest2, MultiSelect2:

• Fix fill prop, which did not work and was a regression from the V1 components
• This was done by migrating to the Popover2 renderTarget API, and has the added benefit of collapsing the DOM rendered by the components
  • ⚠️ This is a slightly breaking change, but we don't expect any real consumers using these component in production yet, so it's ok
• Also improved the docs examples for these components so that they clearly demonstrate disabled, fill, matchTargetWidth props

Select2, MultiSelect2:

• Fix matchTargetWidth styling so that the width of the popup menu is no longer constrained

MultiSelect2:

• Add support for disabled?: boolean prop

Reviewers should focus on:

No regressions, passing test suite

Screenshot

[blueprint-bot]

revert margin change

Previews: documentation | landing | table | demo

[blueprint-bot]

Fix typedef

Previews: documentation | landing | table | demo

[blueprint-bot]

fix test

Previews: documentation | landing | table | demo

[adidahiya]

there's a bug with the min width of the popover when matchTargetWidth={true}:

[adidahiya]

also disabled is not working for MultiSelect2:

[blueprint-bot]

Fix this.state.isOpen references

Previews: documentation | landing | table | demo