refactor(gradle-wrapper): simplify utils and related tests

[Churro]

Changes

Post-processing to #31319:

• getJavaConstraint()
  • extract major for better readability and change >= to === in places where the condition can never be >=
  • remove no longer needed GlobalConfig.set({ binarySource: 'docker' }); from tests and consolidate them
• extractGradleVersion()
  • use multi-line regex instead of line-by-line parsing
  • add real tests so that utils by itself now has full coverage

Context

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 38.85.1 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 38.85.1

Your semantic-release bot 📦🚀