CLI: Refactor help output into categorized chunks

[Devesh99]

The current --help output for spirv-cross is very large, which can be overwhelming for users. This PR refactors the help system to provide a more organized experience.

Changes

• Implemented categorized help flags: --help-glsl, --help-msl, --help-hlsl, and --help-obscure.
• Added --help-all to display the full original help output.
• Updated the default --help output to be more concise:
  • Displays basic usage, backend selection, and common options by default.
  • Lists the new category-specific flags for detailed language options.

Fixes #2601

[CLAassistant]

All committers have signed the CLA.

[HansKristian-Work]

Seems useful, yes.