Choose your own font and size (#1154)

* Refactor text layout: don't need &Fonts in all functions
* Replace indexing in Fonts with member function
* Wrap Fonts in a Mutex
* Remove mutex for Font::glyph_info_cache
* Remove RwLock around Font::characters
* Put FontsImpl and GalleyCache behind the same Mutex
* Round font sizes to whole pixels before deduplicating them
* Make TextStyle !Copy
* Implement user-named TextStyle:s
* round font size earlier
* Cache fonts based on family and size
* Move TextStyle into egui and Style
* Remove body_text_style
* Query graphics about max texture size and use that as font atlas size
* Recreate texture atlas when it is getting full

egui_web/src/painter.rs

@@ -1,6 +1,9 @@
 use wasm_bindgen::prelude::JsValue;
 
 pub trait Painter {
+    /// Max size of one side of a texture.
+    fn max_texture_side(&self) -> usize;
+
     fn set_texture(&mut self, tex_id: egui::TextureId, delta: &egui::epaint::ImageDelta);
 
     fn free_texture(&mut self, tex_id: egui::TextureId);