Currently the GC-cause _last_ditch_collection is used for 2 types of full-collections clearing all soft refereces:
1. Last resort when out of metaspace memory
2. WhiteBox initiated full GC

These have not much in common and the GC-cause is strangely named when looking at it meaning. This cause also comes with an unwanted side-effect, it will expand the heap if possible and this is strange since it is not cause by a failed heap-allocation. My proposal is to remove the _last_ditch_collection cause and instead create _wb_full_gc for the WhiteBox-case and _metadata_GC_clear_soft_refs for the out of metaspace case. The idea is that thet will work similar to _last_ditch_collection in every way except for growing the heap.