LibGUI+FontEditor: Move GlyphMapWidget to LibGUI

This will allow us to use this in other apps, such as the upcoming
Character Map. :^)

Userland/Libraries/LibGUI/CMakeLists.txt

@@ -42,6 +42,7 @@ set(SOURCES
     FontPicker.cpp
     FontPickerDialogGML.h
     Frame.cpp
+    GlyphMapWidget.cpp
     GMLAutocompleteProvider.cpp
     GMLFormatter.cpp
     GMLLexer.cpp