Support extracting Java version from pom.xml and build.gradle via java-version-file

[brunoborges]

Summary: Support java-version-file with pom.xml, build.gradle, and build.gradle.kts so setup-java can infer the JDK version without requiring a separate version file.

Background: PR #441 attempted this but is now outdated/conflicted. The idea remains useful and should continue in a fresh implementation.

Proposed behavior: When java-version-file points to one of the supported build files, parse the configured Java target/version and resolve a setup-java compatible version range.

Initial file targets:

• pom.xml
• build.gradle
• build.gradle.kts

Scope:

• Re-implement on current main (do not reuse PR feat: added support to pom.xml and build.gradle #441 branch directly)
• Add parser logic in current version-file flow
• Add unit/e2e coverage for supported patterns
• Update docs for java-version-file support matrix and precedence rules

Out of scope:

• Changing cache behavior
• Backporting old branch history

Reference: PR #441

[brunoborges]

Tracked under the epic #1048 (infer Java version/distribution from project files), which groups the related file-based detection requests for consistent design. This issue stays open as the specific sub-request.