[Vertex AI] Prepare podspec for a CocoaPods release

[andrewheard]

• Renamed FirebaseVertexAI-Docs.not_podspec to FirebaseVertexAI.podspec in preparation for a CocoaPods release
• Removed an extraneous dependency on SharedTestUtilities
• Updated resource loading to handle both SPM and CocoaPods tests

Note: CI and ZipBuilder changes will still be needed before a release.

#no-changelog

[paulb777]

I'm ok for it to be a follow up PR, but a podspec build and tests should be added to CI similar to other products

Also configuration is needed to include in the zip build

Does anything need to change on the docs gen side to find the new path?

[andrewheard]

I'm ok for it to be a follow up PR, but a podspec build and tests should be added to CI similar to other products

Also configuration is needed to include in the zip build

Does anything need to change on the docs gen side to find the new path?

@paulb777 I'm working on adding a pod-lib-lint job similar to the storage one in another PR. Any other tests that should be included as well?

For docs gen, just won't need to manually rename FirebaseVertexAI-Docs.not_podspec to FirebaseVertexAI.podspec first (@morganchen12 please let me know if that's not accurate).

[andrewheard]

I'm ok for it to be a follow up PR, but a podspec build and tests should be added to CI similar to other products
Also configuration is needed to include in the zip build
Does anything need to change on the docs gen side to find the new path?

@paulb777 I'm working on adding a pod-lib-lint job similar to the storage one in another PR. Any other tests that should be included as well?

For docs gen, just won't need to manually rename FirebaseVertexAI-Docs.not_podspec to FirebaseVertexAI.podspec first (@morganchen12 please let me know if that's not accurate).

Note: Added a basic pod-lib-lint job in this PR and verified with Morgan for docs generation (he said this would simplify it for him).

[paulb777]

LGTM thanks