Add in some generic skills for cpp

[AustinBenoit]

Description

Provide details of the change, and generalize the change in the PR title above.

Add in some generic skills for cpp

---

Testing

Describe how you've tested these changes. Link any manually triggered Integration tests or CPP binary SDK Packaging Github Action workflows, if applicable.

Made sure gemini could use them.

---

Type of Change

Place an x the applicable box:

• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

---

Notes

• Bug fixes and feature changes require an update to the Release Notes section of release_build_files/readme.md.
• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

[gemini-code-assist]

Code Review

This pull request introduces four new skill documentation files for the Firebase C++ SDK, covering native build workflows, Doxygen commenting standards, code formatting procedures, and integration test execution. The feedback focuses on correcting the test runner documentation, specifically clarifying the difference between building the SDK and building test apps for Desktop, ensuring manual CMake commands include the necessary SDK directory flag, and maintaining consistent heading capitalization.

[AustinBenoit]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces several new documentation files (skills) for the Firebase C++ SDK, covering build instructions, commenting standards, code formatting, and test runner workflows. A correction was suggested for the code formatting documentation to use the proper absl-py boolean flag syntax for disabling file formatting.