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This replaces the need to include "Implied if $VAR is set" in switch descriptions by detecting and inserting it automatically. For brevity, skips doing so for --debug, --quiet, --verbose, --help by checking @non_global_processed_options, which is empty when global options are processed. Includes a provision for mentioning an additional related flag, as used by brew bundle's --cleanup. This also:

• adds $ to mentioned environment variables (following Use environment variables consistently #19153)
• reorders env: usage to follow description:
• fixes a bug where a deprecated switch's replacement wasn't mentioned in Manpage.md.