project: Track manifest locations per unique manifest locator (#27194)

This pull request paves way for exposing manifest tracking to
extensions.
- Project tree was renamed to manifest tree to better reflect it's
intent (and avoid confusion).
- Language server adapters now provide a name of their *manifest
locator*. If multiple language servers refer to the same locator, the
locating code will run just once for a given path.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

---------

Co-authored-by: Anthony <anthony@zed.dev>

crates/language/src/manifest.rs

@@ -0,0 +1,48 @@
+use std::{borrow::Borrow, path::Path, sync::Arc};
+
+use gpui::SharedString;
+
+use crate::LspAdapterDelegate;
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct ManifestName(SharedString);
+
+impl Borrow<SharedString> for ManifestName {
+    fn borrow(&self) -> &SharedString {
+        &self.0
+    }
+}
+
+impl From<SharedString> for ManifestName {
+    fn from(value: SharedString) -> Self {
+        Self(value)
+    }
+}
+
+impl From<ManifestName> for SharedString {
+    fn from(value: ManifestName) -> Self {
+        value.0
+    }
+}
+
+impl AsRef<SharedString> for ManifestName {
+    fn as_ref(&self) -> &SharedString {
+        &self.0
+    }
+}
+
+/// Represents a manifest query; given a path to a file, [ManifestSearcher] is tasked with finding a path to the directory containing the manifest for that file.
+///
+/// Since parts of the path might have already been explored, there's an additional `depth` parameter that indicates to what ancestry level a given path should be explored.
+/// For example, given a path like `foo/bar/baz`, a depth of 2 would explore `foo/bar/baz` and `foo/bar`, but not `foo`.
+pub struct ManifestQuery {
+    /// Path to the file, relative to worktree root.
+    pub path: Arc<Path>,
+    pub depth: usize,
+    pub delegate: Arc<dyn LspAdapterDelegate>,
+}
+
+pub trait ManifestProvider {
+    fn name(&self) -> ManifestName;
+    fn search(&self, query: ManifestQuery) -> Option<Arc<Path>>;
+}