Epic: Combobox - A new Select component

[joshhunt]

Old Select related issues (which we aim to address with the New Select):

• https://github.com/grafana/grafana/pull/92026
• https://github.com/grafana/grafana/issues/91683
• https://github.com/grafana/grafana/issues/91546
• Unexpected custom value behavior (this might be related to fuzzy searching) https://github.com/grafana/grafana/issues/91176

These tasks cover Act 1. Things intentionally not adressed here, as they will be adressed at a later date (Act 2):

• Fuzzy search

### Tasks
- [x] Evaluate Downshift vs Floating UI for base
- [ ] https://github.com/grafana/grafana/issues/88897
- [ ] https://github.com/grafana/grafana/issues/88898
- [ ] https://github.com/grafana/grafana/issues/89412
- [ ] https://github.com/grafana/grafana/issues/90122
- [x] Loading/disabled/invalid states
- [ ] https://github.com/grafana/grafana/issues/90646
- [ ] https://github.com/grafana/grafana/issues/91255
- [ ] A11y testing
- [ ] https://github.com/grafana/grafana/issues/90645
- [ ] https://github.com/grafana/grafana/issues/91260
- [ ] https://github.com/grafana/grafana/issues/91259
- [ ] https://github.com/grafana/grafana/issues/92051
- [ ] https://github.com/grafana/grafana/issues/92396
- [ ] https://github.com/grafana/grafana/issues/93036
- [ ] https://github.com/grafana/grafana/issues/92404
- [ ] https://github.com/grafana/grafana/issues/93884

### Non-functional requirements
- [ ] Be FAST! for 1 million items (define "fast")
- [x] Must be accessible
- [x] Must work properly in modals and drawers (be portalled)
- [x] Must be easy to test
- [x] Menu placement should always be visible on the screen

### Known issues
- [ ] https://github.com/grafana/grafana/issues/91950
- [ ] https://github.com/grafana/grafana/issues/91952
- [ ] https://github.com/grafana/grafana/issues/92473
- [ ] https://github.com/grafana/grafana/issues/92586
- [ ] https://github.com/grafana/grafana/issues/92849
- [ ] https://github.com/grafana/grafana/issues/94467
- [ ] https://github.com/grafana/grafana/issues/95384
- [ ] https://github.com/grafana/grafana/issues/95385
- [ ] https://github.com/grafana/grafana/issues/95386
- [ ] https://github.com/grafana/grafana/issues/95567
- [ ] https://github.com/grafana/grafana/pull/95573
- [ ] Combobox: Gracefully degrade with many items berfore perfromance issues start
- [ ] https://github.com/grafana/grafana/pull/96458

[tskarhed]

For the Downshift vs Floating UI task, it doesn't really make sense, as Downshfit handles combobox functionality and Floating UI popover behavior.

[tskarhed]

Considerations:

• What should be the default "no value" value? At the moment it is null, but another option could be ''
• What should the behavior be when you set a value which is not present in the list of options?
  • This might tie into custom value