feat: Retarget Ant build to JDK 21 (no code changes)

[devin-ai-integration]

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Description of the Change

Retargets the fork's Ant/NetBeans/Travis build configuration from Java 11 to Java 21 LTS without changing production or test source code.

Changed files:

• release-build.properties: worldwind.jdk=11 → worldwind.jdk=21
• nbproject/project.properties: javac.source/javac.target 11 → 21
• .travis.yml: openjdk11 → openjdk21
• release-build.xml: Javadoc standard API link updated from Java 8 HTTP docs to Java 21 HTTPS docs

Diff summary:

.travis.yml                  | 2 +-
nbproject/project.properties | 4 ++--
release-build.properties     | 2 +-
release-build.xml            | 2 +-
4 files changed, 5 insertions(+), 5 deletions(-)

Baseline metrics captured separately before changes on develop commit 2543c234349c76f4a290e318b49f071ac156d2a0 under JDK 11:

src java files: 1727
new Runnable(): 148
new ActionListener(): 185
new Callable(): 0
new MouseListener(): 2
new KeyListener(): 0
new ChangeListener(): 60
new PropertyChangeListener(): 44
new WindowListener(): 0
instanceof: 1303
@Deprecated: 131
new Integer(: 0
new Double(: 0
new Float(: 0
new Long(: 0
new Boolean(: 0

Build/test verification:

JDK 11 baseline: ant -f release-build.xml
Result: BUILD SUCCESSFUL
JUnit: files=49 tests=435 failures=0 errors=0 skipped=7

JDK 21 foundation: ant -f release-build.xml
Result: BUILD SUCCESSFUL
JUnit: files=49 tests=435 failures=0 errors=0 skipped=7

No source/test changes check:
git diff develop -- src/ test/ testFunctional/ | wc -l
0

Note: both JDK 11 and JDK 21 builds emit the existing external Javadoc warning for the JogAmp URL (https://jogamp.org/deployment/v2.4.0-rc-20200307/javadoc/package-list) but continue to BUILD SUCCESSFUL.

Rationale: Java 21 is the current LTS target and this foundation PR isolates build retargeting from source modernization. Keeping this PR free of source/test edits makes it a clean compatibility gate for follow-on package-scoped modernization PRs.

Devin session: https://app.devin.ai/sessions/36287b7c637242dba0a6a659737d5402

Why Should This Be In Core?

This establishes Java 21 as the build/test baseline for the fork while preserving the existing WorldWind Java API and implementation unchanged.

Benefits

• Enables follow-on Java 21 modernization PRs to branch from a verified JDK 21 foundation.
• Captures auditable Java 11 baseline counts before source modernization begins.
• Confirms the unmodified source and tests pass under JDK 21 with the same JUnit result as JDK 11.

Potential Drawbacks

• CI environments must provide OpenJDK 21.
• Javadoc still depends on the pre-existing JogAmp external documentation URL, which currently emits a fetch warning but does not fail the release build.

Applicable Issues

N/A

Requested by: @jakexcosme

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[devin-ai-integration]

Original prompt from Jake

#``# Overview

Migrate COG-GTM/WorldWindJava from Java 11 to Java 21 LTS. This is a federal-grade, zero-breakage migration with atomic per-package PRs, full test verification before and after, and a rollup audit document. Use parallel child sessions to accelerate. All PRs target the fork's develop branch.

#``# PHASE 0: Pre-Migration Baseline (Sequential — MUST complete before anything else)

#``#``# Step 0.1: Capture Pre-Migration Baseline Metrics
Before ANY changes, on the develop branch with JDK 11:

`#` File count
find src -name "*.java" | wc -l
`#` Anonymous inner class counts
grep -rn "new Runnable()" --include="*.java" src/ | wc -l
grep -rn "new ActionListener()" --include="*.java" src/ | wc -l
grep -rn "new Callable()" --include="*.java" src/ | wc -l
grep -rn "new MouseListener()" --include="*.java" src/ | wc -l
grep -rn "new KeyListener()" --include="*.java" src/ | wc -l  
grep -rn "new ChangeListener()" --include="*.java" src/ | wc -l
grep -rn "new PropertyChangeListener()" --include="*.java" src/ | wc -l
grep -rn "new WindowListener()" --include="*.java" src/ | wc -l
`#` instanceof pattern-match candidates
grep -rn "instanceof " --include="*.java" src/ | wc -l
`#` Deprecated usage
grep -rn "`@`Deprecated" --include="*.java" src/ | wc -l
grep -rn "new Integer(" --include="*.java" src/ | wc -l
grep -rn "new Double(" --include="*.java" src/ | wc -l
grep -rn "new Float(" --include="*.java" src/ | wc -l
grep -rn "new Long(" --include="*.java" src/ | wc -l
grep -rn "new Boolean(" --include="*.java" src/ | wc -l

Save all counts to a file BASELINE-METRICS.txt at the repo root. This is your "before" snapshot.

#``#``# Step 0.2: Run the existing test suite under JDK 11

ant -f release-build.xml

Record pass/fail counts. This establishes that the test suite is green BEFORE migration.

#``# PHASE 1: Foundational JDK 21 Retarget PR (Sequential — Wave 0)

#``#``# Step 1.1: Create branch devin/java21-foundation
Make these changes ONLY (no code changes):

1. **`release-... (12653 chars truncated...)

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