PR Summary

This improves the fg/bg contrast of the progress colors which improves readability in various color schemes. The current colors are particularly poor in the One Half Dark color scheme. The screenshots below show the before (left) and after (right) for both the Campbell (default) color scheme on top and the One Half Dark color scheme on the bottom:

PR Context

This addresses a comment I made on issue #10780, that the progress fg/bg contrast is not great particularly for the One Half Dark color scheme. FWIW I'm not set on these particular colors. It's just that black on yellow provides good contrast in "most" color schemes whereas yellow on dark cyan does not.

We could consider using RGB colors to "fix" the fg/bg progress colors on hosts that SupportsVirtualTerminal. Using ConsoleColor indices is somewhat problematic as you can see above. That would mean the progress colors might not "fit" the current color scheme but OTOH the progress text would have good contrast for better readability. Also, this represents more code change since the current host colors take only ConsoleColors.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: or [ WIP ] to the beginning of the title (the WIP bot will keep its status check at Pending while the prefix is present) and remove the prefix when the PR is ready.
• Breaking changes
  • None
  • OR
  • Experimental feature(s) needed
    • Experimental feature name(s):
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
  • I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
  • OR
  • I have considered the user experience from a tooling perspective and enumerated concerns in the summary. This may include:
    • Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode (which runs in a different PS Host).
    • Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
    • Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
    • Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).