Extension refactor (#20305)

This contains the main changes to the extensions crate from #20049. The
primary goal here is removing dependencies that we can't include on the
remote.


Release Notes:

- N/A

---------

Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
Co-authored-by: Marshall <marshall@zed.dev>

crates/paths/src/paths.rs

@@ -165,6 +165,22 @@ pub fn extensions_dir() -> &'static PathBuf {
     EXTENSIONS_DIR.get_or_init(|| support_dir().join("extensions"))
 }
 
+/// Returns the path to the extensions directory.
+///
+/// This is where installed extensions are stored on a remote.
+pub fn remote_extensions_dir() -> &'static PathBuf {
+    static EXTENSIONS_DIR: OnceLock<PathBuf> = OnceLock::new();
+    EXTENSIONS_DIR.get_or_init(|| support_dir().join("remote_extensions"))
+}
+
+/// Returns the path to the extensions directory.
+///
+/// This is where installed extensions are stored on a remote.
+pub fn remote_extensions_uploads_dir() -> &'static PathBuf {
+    static UPLOAD_DIR: OnceLock<PathBuf> = OnceLock::new();
+    UPLOAD_DIR.get_or_init(|| remote_extensions_dir().join("uploads"))
+}
+
 /// Returns the path to the themes directory.
 ///
 /// This is where themes that are not provided by extensions are stored.