[CodeMirror v6] cm6 autocomplete parity with current editor

[skyash-dev]

Issue:

Fixes #4167

Demo:

Changes:

• fixed active completion item text color.
• updated autocomplete styling for parity with the current editor.
• fixed autocomplete popup appearing behind the console by adjusting z-index.
• disabled Ctrl+Space autocomplete trigger to match current editor behavior.
• preserved tab-based completion acceptance.
• enabled wrapping of ghost completion text to prevent horizontal scrolling.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines
• verified and ensured consistency with the current editor.