[Mono.Profiler.Log] Support MLPD version 13

[Mono.Profiler.Log] Support MLPD version 13

The differences from v14 are small, and given it is the current "stable"
MLPD version, it's worth supporting it. The differences are:

* ImagePointer field not present in v13 Assembly*Event's
* In MonitorEvent, LogMonitorEvent is not in a separate field, but included
  as a flag in the extType field.
* SampleHitEvent's have a type field in v13, which was removed in v14, because
  only cycles samples are emitted.
* MONO_GC_EVENT_{MARK,RECLAIM}_{START,END} were removed in v14
* SampleUnmanagedBinary's SegmentPointer is not based on ptr_base in v13
* In v13, HeapRootsEvent's Attributes is (wrongly) a byte, in v14 this was
  fixed and changed back to a uleb128