inline completions: Add action to toggle inline completions (#16947)

This adds a new action: `editor: toggle inline completions`.

It allows users to toggle inline completions on/off for the current
buffer.

That toggling is not persistent and when the editor is closed, it's
gone.

That makes it easy to disable inline completions for a single text
buffer, for example, even if you want them on for other buffers.

When toggling on/off, the toggling also overwrites any language
settings. So if you have inline completions disabled for Go buffers,
toggling them on takes precedence over those settings.


Release Notes:

- Added a new editor action to allow toggling inline completions
(Copilot, Supermaven) on and off for the current buffer, taking
precedence over any settings.

Co-authored-by: Antonio <antonio@zed.dev>

crates/editor/src/hunk_diff.rs

@@ -782,7 +782,7 @@ fn editor_with_deleted_text(
         editor.set_show_gutter(false, cx);
         editor.scroll_manager.set_forbid_vertical_scroll(true);
         editor.set_read_only(true);
-        editor.set_show_inline_completions(false);
+        editor.set_show_inline_completions(Some(false), cx);
         editor.highlight_rows::<DiffRowHighlight>(
             Anchor::min()..=Anchor::max(),
             Some(deleted_color),