[v4] [core] fix(MenuItem): improve interactive styles

[adidahiya]

Fixes #4985

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

• Update MenuItem colors to match the intended v4 designs
• Move MenuItem "modern colors" style overrides into the default style code in components/menu/

Reviewers should focus on:

• All the different states & props for MenuItem (see new example)
• Select dropdown interactions
• MultiSelect dropdown interactions

Screenshot

[blueprint-bot]

[v4] [core] fix(MenuItem): improve interactive styles

Previews: documentation | landing | table | modern colors demo

[aycai]

I think this makes the most sense in the select context where the MenuItem changes to blue when selected. That said, selected states should include something else like an icon regardless, so this works on its own.

[aycai]

Caught a visual nit - text of root MenuItem changes to default text

:

[adidahiya]

Fixed styles when submenus are open:

[blueprint-bot]

fix submenu styles, add classes to target icons better

Previews: documentation | landing | table | modern colors demo

[adidahiya]

slight regression in custom icon placement:

[blueprint-bot]

Fix icon placement

Previews: documentation | landing | table | modern colors demo