Adds support for 'normal' and 'focus' Style Boxes to Terminal node.
Changes default background color to transparent, with background to be
set by StyleBox.
If background color is not transparent, will draw a background color
rect to cover the entire control over the top of any stylebox. This is
consistent with the behavior of the TextEdit node with regards to theme
colors and styleboxes.
- Inverse mode invert (default) will invert the color in shader.
- Inverse mode swap will simply swap the foreground and background
colors. This is the default behavior of libtsm and GodotXterm v3.
The two shaders use a lot of common logic for co-ordinate and attribute
look up, so it makes sense to use a common include shader for both.
Adds support for the inverse and blink attributes to the foreground shader.
