Cleaning up constant pool cache clearing code

Cleaning up constant pool cache clearing code

Clear constant pool cache entries which are related to
invokehandle/invokedynamic and ones which are unresolved
(have both bytecodes set to 0).

There are two cases when such entries could be non-empty
(have data in f1/f2):
  1. invokedynamic/invokehandle-related entries in which f2 was
     set during constant pool cache initialization.
  2. put/get into static field when class having the field
     is not initialized yet.

Previously, we didn't clear such entries as clearing f2 in
first case results in crash. However, if we don't clear f1
in the second case, we will not be able to initialize class
for the second time (to re-create all enum constants, for
example) as non-empty f2 will cause assertion to fail.

The current implementation uses free bit in constant pool cache
entry to mark all entries with resolved indices (case #1).
The clearing code preserves f2 for all such entries.