Marks static final field of primitive or known immutable type to be
filtered. In theory, these could be critical to state, but that would
be highly irregular.
NOTE - final does not really mean constant, so we only ignore fields
here that are initialized from lexical constants, i.e. a constpool entry.
Others might involve data choice generators
Ignoring constants probably isn't beneficial with the FilteringSerializer
but could be a big win with AbstractingSerializer, which garbage-collects
no-longer-reachable objects--that is, garbage collection in its
representation, not in VM.