Fully deprecate `public_builds` in projects API

What does this MR do and why?

When we changed from public_builds to public_jobs in gitlab-foss!9463 (merged) we missed the PUT and POST endpoints (as per this comment). Internally we still refer to it as public_builds (see here for example – I actually couldn't find where in the models the attribute itself is defined…) and due to the breaking changes policy for the API we will still need to support public_builds as an API parameter. Using the translate_params_for_compatibility() method to support both is a convenient way to achieve consistency in the API without a large refactor.

Fixes #329725 (closed)

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

I used the following API requests to verify the behavior:

# Create new projects
curl -s --request POST --header "PRIVATE-TOKEN: $GITLAB_TOKEN" "http://gdk.test:3000/api/v4/projects" --form "name=test_false" --form "public_jobs=false"
curl -s --request POST --header "PRIVATE-TOKEN: $GITLAB_TOKEN" "http://gdk.test:3000/api/v4/projects" --form "name=test_true" --form "public_jobs=true"

# Update an existing project
curl -s --request PUT --header "PRIVATE-TOKEN: $GITLAB_TOKEN" "http://gdk.test:3000/api/v4/projects/7" --form "public_jobs=true"
curl -s --request PUT --header "PRIVATE-TOKEN: $GITLAB_TOKEN" "http://gdk.test:3000/api/v4/projects/7" --form "public_jobs=false"

# Repeating the same commands with `public_builds` instead of `public_jobs` still works the same in this branch, whereas on the default branch it will _only_ work with `public_builds` and using `public_jobs` would give an error