Implement warning-suppression-mappings

[kadircet]

This is the tracking bug for implementation of warning-suppression-mappings.

• Have an initial version of the implementation for using it at scale.
• Make sure users of DiagnosticsEngine with a VFS are passing it to warning option parsing, rather than falling back to realfilesystem.
• Let it bake for a while, polish for better UX based on feedback and bugs.
• Put together release notes describing the final state.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: kadir çetinkaya (kadircet)

This is the tracking bug for implementation of [warning-suppression-mappings](https://discourse.llvm.org/t/rfc-add-support-for-controlling-diagnostics-severities-at-file-level-granularity-through-command-line/81292).

• Have an initial version of the implementation for using it at scale.
• Let it bake for a while, polish for better UX based on feedback and bugs.
• Put together release notes describing the final state.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: kadir çetinkaya (kadircet)

This is the tracking bug for implementation of [warning-suppression-mappings](https://discourse.llvm.org/t/rfc-add-support-for-controlling-diagnostics-severities-at-file-level-granularity-through-command-line/81292).

• Have an initial version of the implementation for using it at scale.
• Let it bake for a while, polish for better UX based on feedback and bugs.
• Put together release notes describing the final state.

[kadircet]

#112517 for implementation