Context::add_font (#5228)

make it easier to add fonts. 

For example if I want to add a custom FontFamily or if the user wants to
add a Chinese fallback
* [x] I have followed the instructions in the PR template

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/epaint/src/text/mod.rs

@@ -10,7 +10,10 @@ mod text_layout_types;
 pub const TAB_SIZE: usize = 4;
 
 pub use {
-    fonts::{FontData, FontDefinitions, FontFamily, FontId, FontTweak, Fonts, FontsImpl},
+    fonts::{
+        FontData, FontDefinitions, FontFamily, FontId, FontInsert, FontPriority, FontTweak, Fonts,
+        FontsImpl, InsertFontFamily,
+    },
     text_layout::layout,
     text_layout_types::*,
 };