[Toolkit.Graphics] Fix regression on backbuffer resizing  when using Window.AllowUserResizing = true
Add Property IgnoreUnkownCharacters to SpriteFont for completely skipping glyphs which are not present in the fontmap
Invert condition for better readability
Forgot to invert the condition in the last commit
[Toolkit.Graphics] Add event Effect.Initialized useful when using dynamic recompilation of shaders at runtime
merge from origin