Tuning the performance ~20 times faster by caching InjectionMap instances

I have to process ~10,000 JSON objects returned from a RESTful service. The original version of Vanilla.extract() method took 8.5 seconds and it reached our response limitation requirement.

By using the caching, now it takes only ~0.4 second.
`injectionMap` has not been defined inside this `else` block?  Maybe this code could be simplified to:

```
if (!injectionMapCache[targetType]) 
{
    injectionMapCache[targetType] = new InjectionMap();
    addReflectedRules(injectionMapCache[targetType], targetType, Type.forClass(targetType));
}

const injectionMap = injectionMapCache[targetType];
```