Fix ForegroundTextTransformation objects mem leak

[danipen]

To avoid heap mem pressure, we're using an ArrayPool to avoid too many ForegroundTextTransformation allocations.

The issue is that if this class holds a reference to this (TextMateColoringTransformer) via ForegroundTextTransformation.IColorMap interface implementation. This causes all ForegroundTextTransformations that live in memory (in the shared array pool) will be referencing the TextMateColoringTransformer instance, driving a mem leak.

The issue can be avoided by passing the dictionary with the color map to the ForegroundTextTransformation instead of passing an interface.

[danipen]

@Gillibald please could you review these changes?