Introduce InlineCompletionProvider (#9777)

This pull request introduces a new `InlineCompletionProvider` trait,
which enables making `Editor` copilot-agnostic and lets us push all the
copilot functionality into the `copilot_ui` module. Long-term, I would
like to merge `copilot` and `copilot_ui`, but right now `project`
depends on `copilot`, which makes this impossible.

The reason for adding this new trait is so that we can experiment with
other inline completion providers and swap them at runtime using config
settings.

Please, note also that we renamed some of the existing copilot actions
to be more agnostic (see release notes below). We still kept the old
actions bound for backwards-compatibility, but we should probably remove
them at some later version.

Also, as a drive-by, we added new methods to the `Global` trait that let
you read or mutate a global directly, e.g.:

```rs
MyGlobal::update(cx, |global, cx| {
});
```

Release Notes:

- Renamed the `copilot::Suggest` action to
`editor::ShowInlineCompletion`
- Renamed the `copilot::NextSuggestion` action to
`editor::NextInlineCompletion`
- Renamed the `copilot::PreviousSuggestion` action to
`editor::PreviousInlineCompletion`
- Renamed the `editor::AcceptPartialCopilotSuggestion` action to
`editor::AcceptPartialInlineCompletion`

---------

Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Kyle <kylek@zed.dev>
Co-authored-by: Kyle Kelley <rgbkrk@gmail.com>

crates/languages/src/python.rs

@@ -180,7 +180,7 @@ async fn get_cached_server_binary(
 
 #[cfg(test)]
 mod tests {
-    use gpui::{Context, ModelContext, TestAppContext};
+    use gpui::{BorrowAppContext, Context, ModelContext, TestAppContext};
     use language::{language_settings::AllLanguageSettings, AutoindentMode, Buffer};
     use settings::SettingsStore;
     use std::num::NonZeroU32;