VariableSelect: Multi select design update and behavior improvements

[torkelo]

• [x] Show selected values in the list of options
• [x] Show a checkbox to mark the selection state of a variable value
• [x] Preserve search query after selecting an item (Depends on https://github.com/grafana/grafana/pull/87013)

https://github.com/grafana/scenes/assets/10999/aa29e3f2-1745-4e8f-9dfd-17d4f7428565

📦 Published PR as canary version: 4.14.0--canary.709.8892811931.0

:sparkles: Test out this PR locally via: ```bash npm install @grafana/scenes@4.14.0--canary.709.8892811931.0 # or yarn add @grafana/scenes@4.14.0--canary.709.8892811931.0 ```

[torkelo]

@dprokop updated the group by variable as well

[grafanabot]

:rocket: PR was released in v4.17.0 :rocket: