Extract InlineCompletionProvider to its own crate (#20935)

This PR extracts the `InlineCompletionProvider` trait and its related
types out of `editor` and into a new `inline_completion` crate.

By doing so we're able to remove a dependency on `editor` from the
`copilot` and `supermaven` crates.

We did have to move `editor::Direction` into the `inline_completion`
crate, as it is referenced by the `InlineCompletionProvider`. This
should find a better home, at some point.

Release Notes:

- N/A

crates/editor/src/editor.rs

@@ -28,7 +28,6 @@ mod hover_popover;
 mod hunk_diff;
 mod indent_guides;
 mod inlay_hint_cache;
-mod inline_completion_provider;
 pub mod items;
 mod linked_editing_ranges;
 mod lsp_ext;
@@ -87,7 +86,8 @@ pub(crate) use hunk_diff::HoveredHunk;
 use hunk_diff::{diff_hunk_to_display, ExpandedHunks};
 use indent_guides::ActiveIndentGuidesState;
 use inlay_hint_cache::{InlayHintCache, InlaySplice, InvalidationStrategy};
-pub use inline_completion_provider::*;
+pub use inline_completion::Direction;
+use inline_completion::{InlayProposal, InlineCompletionProvider, InlineCompletionProviderHandle};
 pub use items::MAX_TAB_TITLE_LEN;
 use itertools::Itertools;
 use language::{
@@ -273,12 +273,6 @@ enum DocumentHighlightRead {}
 enum DocumentHighlightWrite {}
 enum InputComposition {}
 
-#[derive(Copy, Clone, PartialEq, Eq)]
-pub enum Direction {
-    Prev,
-    Next,
-}
-
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum Navigated {
     Yes,