`literalExpression` is intended just to signify code that needs to stay
a string that gets represented exactly as-is for docs. It has been
misused heavily and people get confused repeatedly on when or not to use
it because of the rampant misuse.
Add support for managing Copilot CLI global instructions via programs.github-copilot-cli.context, written to copilot-instructions.md under COPILOT_HOME.
Also manage custom agents and skills from inline definitions, file paths, and directories, with focused tests and a news entry covering the new options.
