bug6316: upgrade Eclipse Tycho from 4.0.12 to 5.0.4

Tycho 4.0.x is end-of-life (4.0.13 was the final release); upstream
recommends migrating to the 5.x main line. Tycho 5.x requires Java 21+ as
its runtime VM, which release.yml already satisfies (Maven runs on JDK
25), and still targets the Maven 3.9.x line, so the existing Maven 3.9.11
pin remains valid.

Only java/pom.xml is bumped. The standalone java/com.amazon.aws.aws-java-api
module is deliberately left at Tycho 1.7.0: it builds its local p2 repo
under JDK 8, and Tycho 5.x cannot run on Java 8.

This is an initial probe to see how the release build reacts; serialization/
replication validation (see Bugzilla 3859 note in java/pom.xml) still pending.

Assisted-By: Claude Opus 4.8

java/pom.xml

@@ -36,7 +36,7 @@
          When adjusting tycho-version here, also make sure to adjust it accordingly
          in java/com.amazon.aws.aws-java-api/pom.xml
      -->
-    <tycho-version>4.0.12</tycho-version>
+    <tycho-version>5.0.4</tycho-version>
     <toolchains-version>3.2.0</toolchains-version>
     <gwt.version>2.12.4</gwt.version>
     <!-- gwt-maven-plugin is typically in sync with the GWT version. But sometimes versions need extra time after a new GWT release. -->