Add file_finder module

Still need to wire up key bindings to make it toggle.

Co-Authored-By: Antonio Scandurra <me@as-cii.com>

gpui/src/lib.rs

@@ -18,4 +18,7 @@ pub mod platform;
 pub use pathfinder_color as color;
 pub use pathfinder_geometry as geometry;
 pub use platform::Event;
-pub use presenter::*;
+pub use presenter::{
+    AfterLayoutContext, Axis, EventContext, LayoutContext, PaintContext, SizeConstraint,
+    Vector2FExt,
+};