Implement Java Platform Module System (JPMS) for all ODF Toolkit artifacts:
- Add module-info.java for odfdom, validator, and xslt-runner modules
- Configure module exports, requires, and opens directives
- Update Maven plugin configurations for module-aware builds

Changes:
- Add module-info.java for org.odftoolkit.odfdom module
- Add module-info.java for org.odftoolkit.odfvalidator module
- Add module-info.java for org.odftoolkit.odfxsltrunner module
- Fix test configurations: useModulePath=false for Surefire/Failsafe plugins
- Update maven-failsafe-plugin from 2.22.2 to 3.2.5 in validator
- Add javax.servlet-api as test dependency for validator module
- Fix Jena test classes: replace ModelTestBase with TestCase
- Add validation scripts: validate-modules.sh and validate-modules.bat
- Add MODULE_SYSTEM.md documentation
- Update google-java-format to 1.33.0 for better Java 17+ compatibility
- Add gcf.skip property to allow skipping code formatting if needed
- Format all module-info.java files with google-java-format

All modules compile successfully and pass tests. JARs contain module-info.class
for proper module system support. Backward compatibility maintained for
classpath usage.

Closes: tdf#54