fix(mobile): header menu and Git menu reach a thread's linked pull request#17717

Merge remote-tracking branch 'origin/main' into pr-17717

fix(mobile): header linked-PR entry opens the PR through the shared opener

fix(mobile): linked PR header entry no longer displaces the git icon

fix(mobile): header menu lists the thread's linked pull requests

fix(mobile): git menu opens a linked PR that isn't on the checkout's ref