Add compiler tests for built-in AST transforms

[eric-milles]

There are currently compiler tests for a few of the most venerable AST transforms. For the tested transforms, there could be many more cases covered (options that exist or have been added recently or other variations). For the untested transforms, tests should be added. This could also provide a good opportunity to learn how a particular transform works and can be applied.

Consult https://github.com/groovy/groovy-eclipse/blob/master/base-test/org.eclipse.jdt.groovy.core.tests.compiler/src/org/eclipse/jdt/groovy/core/tests/xform/package.html for an updated list of needs. Here is a snapshot at the time this issue was created: