GuiContainer key and mouse handler methods return true even when input is not handled

In 1.13.2 the key and mouse handler methods for GUIs return `true` when the input is handled, basically so the input event is "consumed" and other things don't use it.

Most GUIs return the right value, but `GuiContainer#keyPressed` and `GuiContainer#mouseClicked` (mcp names ) always returns `true`, and so they do not report if they actually handled the input or not.