Make default text size configurable in Settings

graphics/src/backend.rs

@@ -25,6 +25,9 @@ pub trait Text {
     /// [`ICON_FONT`]: #associatedconst.ICON_FONt
     const CHECKMARK_ICON: char;
 
+    /// Returns the default size of text.
+    fn default_size(&self) -> u16;
+
     /// Measures the text contents with the given size and font,
     /// returning the size of a laid out paragraph that fits in the provided
     /// bounds.

graphics/src/widget/text.rs

@@ -20,7 +20,9 @@ where
 {
     type Font = Font;
 
-    const DEFAULT_SIZE: u16 = 20;
+    fn default_size(&self) -> u16 {
+        self.backend().default_size()
+    }
 
     fn measure(
         &self,