widget/material: allow configuring default typeface on theme

This commit introduces the material.Theme.Face field, which will automatically
populate the Font.Typeface in every text widget created using a constructor function
in package material.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/material/editor.go

@@ -33,7 +33,10 @@ type EditorStyle struct {
 
 func Editor(th *Theme, editor *widget.Editor, hint string) EditorStyle {
 	return EditorStyle{
-		Editor:         editor,
+		Editor: editor,
+		Font: font.Font{
+			Typeface: th.Face,
+		},
 		TextSize:       th.TextSize,
 		Color:          th.Palette.Fg,
 		shaper:         th.Shaper,