Better Identifier Under Caret & Search Result Backgrounds

[Unthrottled]

Description

• Removed searchResultBackground and replaced with foldedTextBackground
• Added a new color identifierHighlight which contrasts with the editor background.
• And a bunch of other small things.

I did this for all 44 themes

😅

Motivation and Context

Closes #370

Screenshots (if appropriate):

Before	After

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project (./gradlew check passes clean).
  • Tip: If you have lint issues just run ./gradlew :ktlintMainSourceSetFormat.
• I updated the version.
• I updated the changelog with the new functionality.