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/copilot/Cargo.toml

@@ -29,14 +29,14 @@ anyhow.workspace = true
 async-compression.workspace = true
 async-tar.workspace = true
 chrono.workspace = true
-collections.workspace = true
 client.workspace = true
+collections.workspace = true
 command_palette_hooks.workspace = true
-editor.workspace = true
 fs.workspace = true
 futures.workspace = true
 gpui.workspace = true
 http_client.workspace = true
+inline_completion.workspace = true
 language.workspace = true
 lsp.workspace = true
 menu.workspace = true
@@ -44,12 +44,12 @@ node_runtime.workspace = true
 parking_lot.workspace = true
 paths.workspace = true
 project.workspace = true
+schemars = { workspace = true, optional = true }
 serde.workspace = true
 serde_json.workspace = true
-schemars = { workspace = true, optional = true }
-strum.workspace = true
 settings.workspace = true
 smol.workspace = true
+strum.workspace = true
 task.workspace = true
 ui.workspace = true
 util.workspace = true