Introduce a New assistant: insert into editor Action (#13467)

This implements the functionality (paired with @as-cii), but we weren't
sure what the clearest name would be for the action. It's essentially
the inverse of "quote selection" - but what's the opposite of quoting
the selection?

One idea:
* Rename "quote selection" to "Insert **into** assistant"
* Name this "Insert **from** assistant"

Release Notes:

- Added action to insert from assistant into editor (default keybinding:
`cmd-<` on macOS, `ctrl-<` on Linux)

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Bennet <bennet@zed.dev>

crates/assistant/src/assistant.rs

@@ -43,6 +43,7 @@ actions!(
         Split,
         CycleMessageRole,
         QuoteSelection,
+        InsertIntoEditor,
         ToggleFocus,
         ResetKey,
         InlineAssist,