GROOVY-5366 unable to add assertions via compile time transform
Fix a bug in JsonBuilder.toPrettyString() for zero-length strings.

Zero-length strings are represented in JSON as a pair of double-quotes
(e.g. "").  This is actually a java.lang.String of length=2.  The old
logic attempted to strip the leading & trailing quotes (either single or
double) using a range of (1..-2), which fails for length=2 strings (it
just reverses the 2 chars).  Replaced with a call to
String.substring( 1, size()-1 ).
GROOVY-5925 Casting map as Random results in java.lang.VerifyError
GROOVY-5932 fix covariance defaultargument problem. The code did modify the modifiers if methods nodes not belonging to it. This part of the code has probably more bugs than just this, but this fix will help limit the problem
GROOVY-5933: @TypeChecked$TypeCheckingInfo is added to constructors
GROOVY-5933: @TypeChecked$TypeCheckingInfo is added to constructors (minor tweaks)