GROOVY-6917: additional cleanup for @Category combined with @CompileStatic
minor refactor: remove some unused imports and expand some * imports (expansion was just where optimize imports made such a change for files having unused imports)

Conflicts:
	src/main/org/codehaus/groovy/antlr/java/Java2GroovyProcessor.java
	src/main/org/codehaus/groovy/transform/stc/GroovyTypeCheckingExtensionSupport.java
merge tweak
GROOVY-6916: Avoid stack overflow when rendering templates and improve the syntax for in-string rendering