pasting code block in chat (#234301)

* first pass code block paste

* added better styling

* some more work

* revert

* added better architecture

* cleanup

* remove unused check

* more clenaup

* use correct URI thing

* new opaque control, new chat request variable type for pastes

* fix hierach type

* fixtypoo

* address more comments

* more cleanup, fix title

* fix merge conflcit

* smol cleanup

* fix compile/hygiene

* i always forget to localize :(

* an actual merge conclift fix

* add create model referencing