RFR: 8332139: SymbolTableHash::Node allocations allocates twice the required memory

[Axel Boldt-Christmas]

The symbols are inline and allocated together with the ConcurrentHashTable (CHT) Nodes. The calculation used for the required size is `alloc_size = size + value.byte_size() + value.effective_length();`

Where
  * `size == sizeof(SymbolTableHash::Node) == sizeof(void*) + sizeof(Symbol)`
  * `value.byte_size() == dynamic_sizeof(Symbol) == sizeof(Symbol) + <bytes beyond object>`
  * `value.effective_length() == dynamic_sizeof(Symbol) - sizeof(Symbol) == <bytes beyond object>`

So `alloc_size` ends up being `sizeof(void*) /* node metadata */ + 2 * dynamic_sizeof(Symbol)`

Because using the CHT with dynamically sized (and inlined)  types requires knowing about its implementation details I chose to make the functionality for calculating the the allocation size a property of the CHT. It now queries the CHT for the node allocation size given the dynamic size required for the VALUE. 

The only current (implicit) restriction regarding using  dynamically sized (and inlined) types in CHT is that the _value field C++ object ends where the Node object ends, so there is not padding bytes where the dynamic payload is allocated. (effectively `sizeof(VALUE) % alignof(Node) == 0` as long as there are no non-standard alignment fields in the Node metadata).  I chose to test this as a runtime assert that the _value ends where the Node object ends, instead of a static assert with the alignment as it seemed to more explicitly show the intent of the check. 

Running testing tier1-7

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Commit messages:
 - 8332139: SymbolTableHash::Node allocations allocates twice the required memory

Changes: https://git.openjdk.org/jdk/pull/19214/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19214&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332139
  Stats: 22 lines in 4 files changed: 17 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/19214.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19214/head:pull/19214

PR: https://git.openjdk.org/jdk/pull/19214