feat: improve tooltip text for disabled languages

Description

This adds specific tooltip text for when Code Suggestions is supported but not enabled for the current editor language.

This only has an effect when "gitlab.featureFlags.languageServer": false. The Language Server counterpart to this MR is in development.

Related Issues

Resolves #1430 (closed)

How has this been tested?

1. Set "gitlab.featureFlags.languageServer": false in your user settings.
2. Open a file written in a supported language
3. Note the tooltip says that Code Suggestions are enabled
4. Disable that language (e.g., via the Toggle Code Suggestions for current language command)
5. Note the tooltip says that Code Suggestions are disabled
6. Open a file written in an unsupported language
7. Note that the tooltip says that Code Suggestions are not supported for current language

Screenshots (if appropriate)

Before	After
simplescreenrecorder-2024-08-05_18.57.22	simplescreenrecorder-2024-08-05_17.57.23

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes

Closes #1430 (closed)