refactor: resolve function regions during build phase to fix VPC connectors

[wandamora]

This moves the resolution logic to be before we resolve the build to a backend to set the defaults in functions, and the correct region can be known when building the VPC connector identfier.

Scenarios Tested

Create function with VPC connector
firebase deploy --only functions on 15.16.0
Update function and use local firebase-tools build
firebase deploy --only functions
Update was successful.

[gemini-code-assist]

Code Review

This pull request refactors the region resolution logic for Cloud Functions, shifting the resolution process from the Backend representation to the Build representation. This allows for correct VPC connector string construction earlier in the deployment process. The new resolveDefaultRegionsForBuild function integrates existing region matching and trigger-based resolution. Review feedback identifies a violation of the style guide regarding the use of the any type and suggests including the endpoint ID in resolver calls to avoid potential issues. Additionally, a suggestion was made to use falsy checks for array length in accordance with project conventions.

[shettyvarun268]

LGTM

[shettyvarun268]

Might want to rebase this PR to take in Joe's changes for the test cases failing.