Perfect FreeType-based outlines for DynamicFonts

- Implement outlines based on FreeType Stroker API. This allows
  artifact-free results, similar to what you will see in Web or any text
  editing tools. Outline is a part of DynamicFont rather than Label,
  because outlines have to be baked into the font's atlas. Font has a
  default outline_color and a Label can specify font_outline_modulator
  that will be multiplied with the Font's color to get the final result.

- draw_char now has to be called twice to fully render a text - first
  with p_outline == true for each character and then with
  p_outline == false for each character.

- Number of draw-calls is reduced from 5 to 2 per outlined character.

- Overall cleanup of DynamicFont code, extracted duplicated code pieces
  into separate methods.

- The change is backward-compatible - Labels still have outline
  properties that work exactly as they worked before.

Closes #16279.

editor/output_strings.cpp

@@ -87,6 +87,7 @@ void OutputStrings::_notification(int p_what) {
 			float h_ofs = (int)h_scroll->get_value();
 			Point2 icon_ofs = Point2(0, (font_height - (int)icon_error->get_height()) / 2);
 
+			FontDrawer drawer(font, Color(1, 1, 1));
 			while (E && ofs.y < (size_height - (int)margin.y)) {
 
 				String str = E->get().text;