FastStringUtils does not work in an OSGi environment

Using the FastStringUtils does not work in an OSGi environment. The FastStringUtils will be called by the classloader of another bundle, making the code at https://github.com/apache/groovy/blob/master/subprojects/groovy-json/src/main/java/org/apache/groovy/json/internal/FastStringUtils.java#L39 not find the default service loader.

To counter this, I'd like to propose to at least fall back to the DefaultFastStringService when no FastStringServiceFactory is found