Gutter icon updates

[Lootwig]

Description

• Allow disabling inline highlighting (gutter only)
• Add border to gutter icons for increased contrast

Motivation and Context

• Inline highlighting doesn't work well when the colors used cover a wide dynamic range
• Gutter icons have low visibility when similar to brightness of gutter background

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Non-Functional Change (non-user facing changes)

Checklist:

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