Add JPMS support for JsonTemplateLayout

The list of things to be done are as follows:

1. Create src/main/java/module-info.java in log4j-jtl module
2. Remove automatic module from log4j-jtl/pom.xml
3. Create log4j-jtl-test module
   1. Move log4j-jtl/src/test to log4j-jtl-test/src/test
   2. Move utility classes from src/test to src/main
   3. Move all classes from .jtl package to .jtl.test package
   4. Update log4j-jtl-test/pom.xml to reflect the package path change
   5. Fix log4j-jtl testJar dependency in log4j-perf