RFR (S) Allow ResourceHashtable size to be specified at runtime

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8213587
http://cr.openjdk.java.net/~iklam/jdk12/8213587-configurable-resource-hash.v01/

TL;DR: -- add a subclass to ResourceHashtable to allow the table size to be
           dynamically specified when the table is constructed.


         *** C++ template guru alert ***


I don't know much about C++ templates, so my attempt on doing this may be
ill-advised.

I *think* that with my patch, the performance of existing code, which uses
a statically-defined SIZE,  should not be affected, as the C++ compiler
should be able to constant-propagate and reduce the new code:

   ALWAYSINLINE unsigned size() const {
     if (SIZE != CONFIGURABLE_SIZE) {
       return SIZE;
     } else {
       return _configured_table_size;
     }
   }

   ALWAYSINLINE Node** get_table() const {
     if (SIZE != CONFIGURABLE_SIZE) {
       return (Node**)(&_static_table[0]);
     } else {
       return _configured_table;
     }
   }

   Node** lookup_node(unsigned hash, K const& key) {
     unsigned index = hash % size();    <-----
     Node** table = get_table();
     Node** ptr = &table[index];   <-----

back to the old code:

   Node** lookup_node(unsigned hash, K const& key) {
     unsigned index = hash % SIZE;      <-----
     Node** ptr = &_table[index];       <-----


If anyone has a better way of doing this, I'd love to hear it!

Thanks!
- Ioi