refactor: Make workflows reusable for external repositories

This change refactors the GitHub Actions workflows to support 'workflow_call' triggers.

Key changes:
- Added 'workflow_call' triggers to all relevant workflows.
- Replaced hardcoded 'phlex' references with dynamic repository information.
- Added inputs to configure checkout paths, build matrices, and skip relevance checks.
- Ensured workflows remain backward-compatible with existing triggers.
- Fixed an issue with constructing CMake sanitizer options by correctly extracting the repository name.
- Corrected the relevance check in `actionlint-check.yaml` to handle pull request context from `workflow_call`.

This allows the workflows to be called from external repositories, improving their reusability and portability.

Author: google-labs-jules[bot]