feat(editor): add support for static span colors

[itsaky]

This PR adds support for static color spans in the editor.

Static color spans

Static color spans are spans whose background and foreground colors are pre-defined during the source code analysis. Two new color IDs have been added to EditorColorScheme :

• STATIC_SPAN_BACKGROUND -> for the background
• STATIC_SPAN_FOREGROUND -> for the foreground

Here is a demo implementation of the feature (the color is same for all string tokens) :

Known issues

There is only one issue that I have noticed and it is not specifically related to this feature addition :

If a span has a custom background color and if that span is in the selection region, the span background color hides the selected text background color. This happens because the selection is drawn before the span (i.e. the span color overlaps the selection color).

This can be resolved by either :

• Draw the selection region after the span background is drawn.
• Skip drawing the span background if it is in the selection region.
• Invert the span background color by if it is in the selection region.

The last two approaches should also handle the case where the span is partially in the selection region. These two approaches should be preferred in my opinion.

Additional changes

A new class (SpanPool) has been added to recycle and reuse the Span objects (and its subclasses by creating multiple pools). The implementation of the pool is same as what was being used earlier for caching. However, multiple pools can now be created with different capacities.

[Rosemoe]

Thanks for your contributions!