[RFC] Global search API (#64284)

* initial file import

* update types

* update RFC PR number

* first draft complete

* draft v1.1.0

* initial self review

* nits and comments

* add 'preference' option

* change meta type to Record<string, Serializable>

* specify cancellation

* remove generic for GlobalSearchResponse, use distinct type on client and server

* use plain string instead of enum for GlobalSearchResult.type

* remove terminology from unresolved questions

* update pros/cons of core vs plugin

* GS is exposed from a plugin instead of core

* remove the server.publicAddress proposal, return mixed abs url / rel paths instead

* distinguish result type between GS api and result providers

* return batched results, no longer sort

* remove request from GlobalSearchProviderContext

* add maxResults to GlobalSearchProviderFindOptions

* nit/typo