What?

This PR contains cleanups/refactors based on comments made on previous PRs when working on the page.getBy* APIs.

Why?

Here are the list of comments:

• Cleanup the injected script #4933
• Add aria-labelledby test for getByRole #4956
• Add getByAltText in the browser module #4881 (comment)
• https://github.com/grafana/k6/pull/4904/files#r2223038986
• Add getByLabel in the browser module #4890 (comment)
• Add getByLabel in the browser module #4890 (comment)
• https://github.com/grafana/k6/pull/4890/files#r2223067227
• Add getByTitle in the browser module #4910 (comment)
• Add getByTitle in the browser module #4910 (comment)

Checklist

• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests for my changes.
• I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• I have added the correct milestone and labels to the PR.
• I have updated the release notes: link
• I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

Related PR(s)/Issue(s)

#5049 (comment)
#4933
#4956
#4964