Allow deselect when renderSelectedChoices enabled

[godismyjudge95]

Description

Drafting this PR as I am not sure if you would want to follow a different approach. If this looks good I can try to add tests.

There have been a few requests to allow for deselecting items via the dropdown when the renderSelectedChoices option is enabled. #804 #884

I ran across this issue myself while needing to keep a multiselect box footprint minimal (it grows to be pretty large when selecting a few options).

This PR has 3 parts:m

• highlight selected choices in the dropdown when renderSelectedChoices is enabled
• allow clicking on a selected choice in the dropdown to deselect the choice
• add a new renderItems boolean option to disable the "pills" in the multiselect input to allow one to only select/deselect via the dropdown

Screenshots (if appropriate)

Example of having both renderSelectedChoices: 'always' and renderItems: false

Types of changes

• [x] Chore (tooling change or documentation change)
• [ ] Refactor (non-breaking change which maintains existing functionality)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• [x] My code follows the code style of this project.
• [ ] I have added new tests for the bug I fixed/the new feature I added.
• [ ] I have modified existing tests for the bug I fixed/the new feature I added.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.