RFR (M) 8213346 Re-implement shared dictionary

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8213346
http://cr.openjdk.java.net/~iklam/jdk12/8213346-shared-dict-using-compact-hashtable.v01/

Please review a long overdue cleanup of how the classes are indexed in 
the CDS
archive.

[1] Use CompactHashtable which is more space efficient than Dictionary.

[2] Space saving:

     + For each shared class, we used to store a fixed-size record in
       SharedDictionaryEntry. That information is now stored in a
       variable-length structure (see RunTimeSharedClassInfo).

     + Verifier constraints are now stored using u4 instead of Symbol*.

Total space saving is about 45KB for the default CDS archive.

[4] We had scattered code that checked whether a class should be archived
     or not. E.g., checking for code signers, JFR, etc. Now this is 
checked inside
     a consolidated function SystemDictionaryShared::should_be_excluded()

[5] Now we have 2 separate hashtable to look up shared classes: one for the
     built-in classes and the other for unregistered classes. This 
simplifies the
     lookup logic and is also faster.

[6] A lot of old code was deleted. There's a net change of about -250 
lines of C
     code.

TESTING:

I am running hs-tiers 1/2/3/4

Thanks
- Ioi