Fix Tycho build for native fragments and make multi-platform plugins buildable

[strimo378]

Motivation

• The Tycho/Tycho+Maven build failed because native fragment bundles were packaged as plain OSGi bundles without proper Eclipse/Tycho packaging, lacked OSGi metadata and native artifacts, and Tycho validation rejected cross-platform native entries.
• Make the reactor build reproducible in CI and allow the feature/p2 assembly to resolve by producing proper Eclipse plugin artifacts and shipping placeholder native libs until real native binaries are built.

Description

• Converted bundle modules to Tycho eclipse-plugin packaging for com.emmtrix.isl.core, com.emmtrix.isl.jni, and all com.emmtrix.isl.native.* fragments and added minimal OSGi manifests and build.properties so Tycho can package them.
• Added placeholder native artifacts under each fragment at src/main/resources/native/<os>/<arch>/ (isl_wrapper.dll, libisl_wrapper.so, libisl_wrapper.dylib) to satisfy Bundle-NativeCode requirements until real CMake-built binaries are produced.
• Prevented Tycho classpath/native validation from failing fragments on non-matching hosts by disabling the default validate-classpath execution for the native fragment modules via a tycho-compiler-plugin execution override.
• Enabled reactor dependency wrapping for the Tycho target platform by adding target-platform-configuration with <pomDependencies>wrapAsBundle</pomDependencies> to the parent pom.xml so reactor modules can be resolved by the feature build.

Testing

• Ran a full Tycho/Maven build with mvn -V -B -DskipTests=false clean verify, and the reactor build completed successfully (the JUnit/Tycho test modules ran during the build).
• The included smoke and end-to-end tests executed as part of the build (tests/java, tests/osgi-smoke, tests/p2-e2e) and reported passing in the build output.
• The Tycho feature and update-site packaging steps completed and produced the p2 ZIP artifact in releng/com.emmtrix.isl.site/target during the successful run.

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Codex Task