feat: Add validation for function prefixes and source/prefix pairs

[taeold]

This change introduces two new validation rules for function configurations in firebase.json:

1. The prefix property, if specified, must only contain lowercase letters, numbers, and hyphens.
2. The combination of source and prefix must be unique across all function configurations.

These changes ensure that function deployments with prefixes are valid and that there are no conflicts when deploying multiple functions from the same source directory.

[gemini-code-assist]

Summary of Changes

Hello @taeold, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the flexibility and robustness of Firebase Functions configurations by introducing support for function name prefixes. The primary goal is to enable developers to define and deploy multiple distinct function configurations from a single source directory, while simultaneously enforcing strict validation rules on these prefixes to prevent naming collisions and ensure deployment integrity. This change impacts both the configuration schema and the core logic for building, deploying, and emulating functions.

Highlights

• New prefix property for Functions: Introduced a new optional prefix property for function configurations within firebase.json. This allows developers to define a prefix that will be prepended to the function's ID during deployment, enabling more flexible naming conventions and supporting multiple function configurations from the same source directory.
• Prefix Validation Rules: Implemented strict validation for the new prefix property. The prefix must now consist only of lowercase letters, numbers, and hyphens, and has a maximum length of 30 characters. This ensures valid and consistent function naming.
• Unique Source/Prefix Combination Enforcement: Added a crucial validation rule that requires the combination of a function's source directory and its prefix to be unique across all function configurations. This prevents naming conflicts when deploying multiple functions that share the same source code but are intended to be distinct entities.
• Emulator and Build Process Integration: Updated the Firebase Functions emulator and the build/deployment pipeline to correctly recognize and apply the new prefix property. This ensures that functions are correctly named and discoverable both during local development and actual deployments.

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[gemini-code-assist]

Code Review

This pull request introduces validation for function prefixes and ensures uniqueness for source/prefix pairs, which is a valuable addition for managing complex function deployments. The implementation is solid and well-tested. I have a few suggestions to enhance the robustness of the validation and improve test coverage. My main concern is with the prefix validation logic, which could allow for invalid function names to be constructed. I've provided a critical-severity comment with a suggested fix for this. I've also suggested a minor code simplification and an additional test case to cover an important edge case. Overall, great work on this feature!