Custom Multiselect

[ElectronicBlueberry]

Supersedes #17269

Replaces the Multiselect used in the tagging component with a custom component.
The custom component renders in a different layer, to prevent z-index layering issues when used inside small components.
It is fully keyboard accessible.

No visual changes.

ping @itisAliRH

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Looks good and works well, thanks @ElectronicBlueberry!

[itisAliRH]

Isn't it better to move this file to the common components?

[ElectronicBlueberry]

Currently it's quite specific to the tag component, as it only implements the Multiselect features used by the tag component. When this gets used in more places, I'd be happy to move it then.