Enable manually editing search context

[beyang]

Adds a button to ContextCell that copies the fetched context items to the previous input as context chips.

manual-context.mov

Outstanding todos:

• Change text from "manually edit context" to "edit context"
• Make work when search intent is detected. Text should be "move results to input"
• Expand search results by default

Test plan

• Use an @repo chip
• Click the "Edit context manually" button
• Verify context items are added to the input

[thenamankumar]

why are we removing the non-repo mentions ?

[beyang]

renamed removeMentions to filterMentions

[PriNova]

After step 3 in the test plan, if asking Cody new with the edited context files, the fetching as context fails and Cody responses with a wild guess.

The issue is, that Cody tries to fetch from sourcegraph.com and fails