Increase initial size of text cache in iced_wgpu

This reduces the amount of cache updates in general when text changes.

The new cache should take 4MB of VRAM. I think this is reasonable for a
modern GUI toolkit. In any case, we should be able to reduce this value in the
future.

wgpu/src/renderer.rs

@@ -74,6 +74,7 @@ impl Renderer {
 
         let glyph_brush =
             GlyphBrushBuilder::using_fonts_bytes(vec![default_font, mono_font])
+                .initial_cache_size((2048, 2048))
                 .build(&mut device, TextureFormat::Bgra8UnormSrgb);
 
         let quad_pipeline = quad::Pipeline::new(&mut device);