Fix or promote leftover TODOs and GPUI APIs (#12514)

fixes https://github.com/zed-industries/zed/issues/11966

Release Notes:

- N/A

crates/gpui/src/platform/test/text_system.rs

@@ -1,50 +0,0 @@
-use crate::{
-    Bounds, DevicePixels, Font, FontId, FontMetrics, FontRun, GlyphId, LineLayout, Pixels,
-    PlatformTextSystem, RenderGlyphParams, Size,
-};
-use anyhow::Result;
-use std::borrow::Cow;
-
-pub(crate) struct TestTextSystem {}
-
-// todo(linux)
-#[allow(unused)]
-impl PlatformTextSystem for TestTextSystem {
-    fn add_fonts(&self, fonts: Vec<Cow<'static, [u8]>>) -> Result<()> {
-        unimplemented!()
-    }
-    fn all_font_names(&self) -> Vec<String> {
-        unimplemented!()
-    }
-    fn all_font_families(&self) -> Vec<String> {
-        unimplemented!()
-    }
-    fn font_id(&self, descriptor: &Font) -> Result<FontId> {
-        unimplemented!()
-    }
-    fn font_metrics(&self, font_id: FontId) -> FontMetrics {
-        unimplemented!()
-    }
-    fn typographic_bounds(&self, font_id: FontId, glyph_id: GlyphId) -> Result<Bounds<f32>> {
-        unimplemented!()
-    }
-    fn advance(&self, font_id: FontId, glyph_id: GlyphId) -> Result<Size<f32>> {
-        unimplemented!()
-    }
-    fn glyph_for_char(&self, font_id: FontId, ch: char) -> Option<GlyphId> {
-        unimplemented!()
-    }
-    fn glyph_raster_bounds(&self, params: &RenderGlyphParams) -> Result<Bounds<DevicePixels>> {
-        unimplemented!()
-    }
-    fn rasterize_glyph(
-        &self,
-        params: &RenderGlyphParams,
-        raster_bounds: Bounds<DevicePixels>,
-    ) -> Result<(Size<DevicePixels>, Vec<u8>)> {
-        unimplemented!()
-    }
-    fn layout_line(&self, text: &str, font_size: Pixels, runs: &[FontRun]) -> LineLayout {
-        unimplemented!()
-    }
-}

crates/gpui/src/platform/test/window.rs

@@ -132,8 +132,8 @@ impl PlatformWindow for TestWindow {
         WindowAppearance::Light
     }
 
-    fn display(&self) -> std::rc::Rc<dyn crate::PlatformDisplay> {
-        self.0.lock().display.clone()
+    fn display(&self) -> Option<std::rc::Rc<dyn crate::PlatformDisplay>> {
+        Some(self.0.lock().display.clone())
     }
 
     fn mouse_position(&self) -> Point<Pixels> {