Add a dedicated action to open files (#22625)

Closes #22531
Closes #22250
Closes #15679

Release Notes:

- Add `workspace::OpenFiles` action to enable opening individual files
on Linux and Windows

crates/gpui/src/platform.rs

@@ -175,6 +175,7 @@ pub(crate) trait Platform: 'static {
         options: PathPromptOptions,
     ) -> oneshot::Receiver<Result<Option<Vec<PathBuf>>>>;
     fn prompt_for_new_path(&self, directory: &Path) -> oneshot::Receiver<Result<Option<PathBuf>>>;
+    fn can_select_mixed_files_and_dirs(&self) -> bool;
     fn reveal_path(&self, path: &Path);
     fn open_with_system(&self, path: &Path);