feat(manager/gradle): enable property accessors for registry URLs

[Churro]

Changes

• Extends the existing support for property accesors to registry URLs
  • name and url of maven repo declarations may be specified as properties (example)
• Ignores as String type casts, occasionally used with properties in Kotlin projects (example)
• Refactoring: Extracts a common URI pattern to reuse across all spots where java.net.URI is expected
  • Idea: For better maintainability, have a common selector for URLs specified directly (ref) or via uri (ref).

Context

• Related to feat(manager/gradle): add support for property accessors #18990

Documentation (please check one with an [x])

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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 34.76.0 🎉

The release is available on:

• GitHub release
• 34.76.0

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