feat(gengapic): add support for AutoPopulatedFields UUID4

[quartzmo]

No description provided.

[noahdietz]

Since we are adding a net new dependency to generated code, can you also include the dep for bazel here: https://github.com/googleapis/gapic-generator-go/blob/main/rules_go_gapic/go_gapic.bzl#L156-L157

"@com_github_google_uuid//:go_default_library" I think should do it.

[quartzmo]

@noahdietz Updated with the UUID dependency, thank you.

I locally ran the bazel targets for the "usual suspects" set of gapic libraries:

bazelisk build //google/cloud/apigeeconnect/v1:apigeeconnect_go_gapic
bazelisk build //google/cloud/asset/v1:asset_go_gapic
bazelisk build //google/cloud/language/v1:language_go_gapic
bazelisk build //google/spanner/v1:spanner_go_gapic
bazelisk build //google/cloud/aiplatform/v1beta1:aiplatform_go_gapic
bazelisk build //google/cloud/compute/v1:compute_go_gapic

[noahdietz]

Suggested change

	p("if req != nil && req.%s == \"\" {", f)
	p("if req != nil && req.Get%s() == \"\" {", f)

But we may want to use buildAccessor to get this string instead of just doing snakeToCmael...

[quartzmo]

Updated with buildAccessor, PTAL, thanks!

[quartzmo]

Please check the update .want files to verify the output now looks good, thanks!

[noahdietz]

I'm sorry @quartzmo I should've been more explicit in my comments

[noahdietz]

LGTM great work and thanks for your patience with my review. Add that test we spoke about offline and you are good to go.