Update all Java version references to align with Java 21 target

[devin-ai-integration]

Description of what I changed

Updates all outdated Java version references across the codebase to align with the project's Java 21 target (already set in the root pom.xml as javaCompilerVersion=21).

Changes:

1. test-module/pom.xml — Updated javaCompilerVersion from 1.8 to 21 so the test module compiles with the same target as the rest of the project.

2. OpenmrsUtil.java — validateJavaVersion() — Replaced the old regex-based check (1\\.[0-7]\\.(.*)) with Runtime.version().feature() < 21. The old regex only rejected Java 1.0–1.7 using the legacy 1.x naming scheme and could never reject Java 8–20 (which use the modern naming scheme like 21.0.1). The new implementation correctly enforces a minimum of Java 21. Updated Javadoc and error message accordingly.

3. README.md — Updated minimum Java version from 8 to 21 in the build prerequisites.

4. tools/pom.xml — Removed both default-tools.jar and mac-tools.jar profiles. These referenced com.sun:tools / tools.jar, which was removed from the JDK in Java 9 (Project Jigsaw). On Java 21 these profiles are dead code — the activation file-exists conditions can never be true.

5. pom.xml — Updated the stale comment on the Java 17 mockito profile that incorrectly referenced Java 8 compatibility. The new comment accurately describes the NullPointerException issue with mockito-core:3.12.4 on Java 17.

Key review points

• validateJavaVersion() rewrite: Uses Runtime.version().feature() (available since Java 10) instead of regex parsing. Verify this is the desired approach vs. other alternatives.
• tools/pom.xml profile removal: Confirm no other module or build step depends on the com.sun:tools artifact declaration.

Issue I worked on

see https://issues.openmrs.org/browse/TRUNK-

Checklist: I completed these to help reviewers :)

• My IDE is configured to follow the code style of this project.
• I have added tests to cover my changes. (If you refactored existing code that was well tested you do not have to add tests)
• I ran mvn clean package right before creating this pull request and added all formatting changes to my commit.
• All new and existing tests passed.
• My pull request is based on the latest changes of the master branch.

Link to Devin session: https://app.devin.ai/sessions/362a17cce8394d50b8e5afdbbc7a9507
Requested by: @dillonvargo

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[devin-ai-integration]

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.