GROOVY-6343: @CompileStatic: can't access static field from nested closures

added non regression test
GROOVY-6343: @CompileStatic: can't access static field from nested closures

removed superfluous line from test
GROOVY-5981: @TypedChecked error when using generics

added non regression test
GROOVY-6751: Error in @TypeChecked when method in both Interface and Superclass

added non regression test
Make it clear that the template engine can be used to render any text based content