vim: Don't show inline completions in normal mode (#17137)

This fixes an annoying bug I ran into, where supermaven completions
would show up in normal mode.

cc @ConradIrwin not sure if this is the best way to fix this, but it
seems like the neatest? On one hand, I didn't want to touch into Vim
from the editor, and on the other I didn't want to add another boolean
on the editor that flips on when in normal mode. So instead I extended
the Addon interface.

Release Notes:

- Fixed inline completions (Copilot or Supermaven) showing up in Vim's
normal mode.

crates/editor/src/editor.rs

@@ -470,6 +470,9 @@ struct BufferOffset(usize);
 // Addons allow storing per-editor state in other crates (e.g. Vim)
 pub trait Addon: 'static {
     fn extend_key_context(&self, _: &mut KeyContext, _: &AppContext) {}
+    fn should_show_inline_completions(&self, _: &AppContext) -> bool {
+        true
+    }
 
     fn to_any(&self) -> &dyn std::any::Any;
 }
@@ -2340,6 +2343,11 @@ impl Editor {
         cx: &AppContext,
     ) -> bool {
         if let Some(provider) = self.inline_completion_provider() {
+            for addon in self.addons.values() {
+                if !addon.should_show_inline_completions(cx) {
+                    return false;
+                }
+            }
             if let Some(show_inline_completions) = self.show_inline_completions_override {
                 show_inline_completions
             } else {