editor: Improve text color in document color highlight

[huacnlee]

Release Notes:

• Improved text color in LSP document color highlight.

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Because highlight ranges are implemented using a paint background, there's no way to control the text color.

I've been thinking about this problem for a long time, want to solve it.

Today, I come up with a new idea. Re-rendering the document color text at the top should solve this problem.

Update 10/6:

The previous version is not good, when we have soft wrap text, that version will not work correct.

Now use exists bg_segments_per_row feature to fix text color.

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[JosephTLyons]

Thanks for the PR @huacnlee - we'll get this reviewed shortly!

[smitbarmase]

Thank you, @huacnlee!