feat: add --resource-name-alias flag to resolve namespace collisions

[ohmayr]

Introduces the --resource-name-alias CLI flag to allow API owners
to safely disambiguate fully qualified resource paths that flatten
to identical method names in the generated client.

The flag accepts mappings in the format resource.path/Name:AliasName.
The configuration is parsed natively into the compiler Options and
injected into the schema models during construction, avoiding global
state mutations.

Example usage in BUILD.bazel:

--resource-name-alias=ces.googleapis.com/Tool:CesTool

Towards: b/505425328

[gemini-code-assist]

Code Review

This pull request introduces a mechanism to resolve resource name collisions in the GAPIC generator via a new --resource-name-alias CLI parameter. Key changes include updating the Options and MessageType classes to handle these aliases and implementing a fail-fast collision detection check that raises a ValueError when conflicts occur. Feedback suggests that the generator should raise an error for malformed alias inputs to ensure fail-fast behavior instead of merely issuing a warning.

[gemini-code-assist]

The use of split(":", 1) correctly handles cases where the resource path itself might contain a colon. However, if the input string does not contain a colon, this will raise a ValueError. If the current logic in the except block returns an empty value, it should be changed to raise a ProgrammingError to ensure fail-fast behavior for unsupported input formats, rather than silently continuing.

References

1. When a function receives parameters of an unsupported type, it should raise an error (e.g., ProgrammingError) instead of silently returning empty values. This ensures fail-fast behavior and prevents potential issues with missing parameter values in database operations.

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