Improve builder value fill

[hduelme]

I changed the generated code to use java switch string matching, if there are more than 3 strings to check. For this I extracted the builder fill code into fillBuilder macro.
I although changed the loop iteration to use entrySet.

[hduelme]

I tested the this improvement with mapstruct and found a small improvement (about 100ms for mapstruct-processor in MapperGem), manly due to the reduction in String comparison.

[filiphr]

This reads way better @hduelme. Thanks a lot for the improvements. I've left some comments.

Apart of the comments, I see that we have a lot of values.get( methodName ) and defaultMethod.getValue(). Won't it be a bit better if we assign them at the beginning of the if / switch?

e.g.

String methodName = defaultMethod.getKey();
switch ( methodName ) {
    case "myClassWithDefault":
        builder.setMyclasswithdefault( GemValue.create( values.get( methodName ), defaultMethod.getValue(), TypeMirror.class ) );
        break;

Would become

String methodName = defaultMethod.getKey();
AnnotationValue defaultValue = defaultMethod.getValue();
AnnotationValue value = values.get( methodName );
switch ( methodName ) {
    case "myClassWithDefault":
        builder.setMyclasswithdefault( GemValue.create( value, defaultValue, TypeMirror.class ) );
        break;

[filiphr]

I tested the this improvement with mapstruct and found a small improvement (about 100ms for mapstruct-processor in MapperGem), manly due to the reduction in String comparison.

That's great

[hduelme]

@filiphr I've addressed your comments. I agree that moving defaultValue and value in front of the switch/if statement improves readability. I've made that change.