RFR 8150607 - Clean up CompactHashtable

[Ioi Lam]

Please review

http://cr.openjdk.java.net/~iklam/jdk9/8150607_cleanup_compact_hashtable.v01/

Bug: Clean up CompactHashtable

     https://bugs.openjdk.java.net/browse/JDK-8150607

Summary of fix:

[1] Instead of reading/writing the table bit-by-bit, which is tedious and
     error prone, use SimpleCompactHashtable::serialize(), which is more
     structural.

[2] Split up the _buckets and _entries into two separate arrays, so the
     dumping and walking code is easier to understand

     (see comments above SimpleCompactHashtable declaration)
     These 2 arrays are now allocated from the RO region (used to be in RW)

[3] Renamed a few things

     COMPACT_BUCKET_TYPE -> TINY_BUCKET_TYPE
         (having something called "compact" in CompactHashtable is 
confusing)

     The old names "dump_table" (actually dumping the buckets) and
     "dump_buckets" (actually dumping the entries) were conflicting with
     terminology used elsewhere. Now the terminology is unified:
         "buckets" = the main index, "entries" = the second level.

     lookup_entry -> decode_entry (it wasn't doing any lookup)

[4] Changed all "*p++" to "array->at_put", so out-of-bounds can be
     checked with assert.

[5] Replaced all juint to u4 (suggested by Coleen)

[6] templatize the iterator (see CompactHashtable::symbols_do ->
     SimpleCompactHashtable::iterate)

[7] I also added a test case using Serviceability Agent -- due to the 
lack of
     a regression test, the walking of the compact hashtable in SA had been
     broken for a while before it was fixed in JDK-8151368, so having a test
     case would make the code more maintainable.

Tests:

     Hotspot JTREG tests

Thanks
- Ioi