Linux: Experiment with CosmicText based Text System (#7539)

This is a rebase of @gabydds text_system updates. with some small
cleanups.

Currently cannot test this as build is not working in linux. Im just
putting it up here before I forget about it.

---------

Co-authored-by: gabydd <gabydinnerdavid@gmail.com>
Co-authored-by: Mikayla Maki <mikayla@zed.dev>

crates/gpui/src/text_system.rs

@@ -725,6 +725,7 @@ pub struct FontMetrics {
     pub(crate) x_height: f32,
 
     /// The outer limits of the area that the font covers.
+    /// Corresponds to the xMin / xMax / yMin / yMax values in the OpenType `head` table
     pub(crate) bounding_box: Bounds<f32>,
 }