Respect Style::override_font_id in RichText (#5310)

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Currently `Style::override_font_id` does not affect widgets with their
`TextStyle` like `Button`s, `ComboBox`es, `CheckBox`es, etc. This PR
fixes this behavior such that all widgets using default configuration of
`RichText` are affected by this setting.
* [x] I have followed the instructions in the PR template

crates/egui/src/widget_text.rs

@@ -380,6 +380,9 @@ impl RichText {
                     || fallback_font.resolve(style),
                     |text_style| text_style.resolve(style),
                 );
+            if let Some(fid) = style.override_font_id.clone() {
+                font_id = fid;
+            }
             if let Some(size) = size {
                 font_id.size = size;
             }