Implement per-workspace C/C++ configurations (#14363)

[Subham-KRLX]

This PR introduces the C_Cpp.configurations setting, allowing users to define C/C++ configurations directly within VS Code workspace or folder settings. This resolves #14363, where multiple workspaces sharing the same folder were forced to share a single c_cpp_properties.json file.

Key Changes

• Precedence Logic: Updated the configuration parser to prioritize C_Cpp.configurations from settings over the local c_cpp_properties.json file.
• Full Parity: The new settings-based configurations support the exact same schema, variable resolution (e.g., ${workspaceFolder}), and sanitization logic as the traditional file-based approach.
• Reactive Updates: Integrated with onDidChangeSettings to ensure IntelliSense/Status Bar UI updates immediately when settings are modified.
• Backward Compatibility: If the new setting is not present, the extension falls back to existing file-based behavior with no disruption.

Verification

• Verified that workspace settings override local c_cpp_properties.json.
• Verified fallback behavior when settings are cleared.
• Confirmed that variable resolution remains consistent across both configuration sources.

Fixes #14363