RFR: 8292383: Create a SymbolHandle type to use for ResourceHashtable

[Coleen Phillimore]

This change creates a SymbolHandle which shares code with TempNewSymbol and moves them to their own header file.  We could expand this use if needed for GrowableArrays and other things where we have some various Symbol increment/decrement refcounts now.  Changed a few ResourceHashtables that take Symbol* keys to use SymbolHandle and verified the refcounts.  Also fixed the gtest.
Tested with tier1-7.

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Commit messages:
 - 8292383: Create a SymbolKey type to use for ResourceHashtable

Changes: https://git.openjdk.org/jdk/pull/10052/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10052&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292383
  Stats: 237 lines in 16 files changed: 108 ins; 82 del; 47 mod
  Patch: https://git.openjdk.org/jdk/pull/10052.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10052/head:pull/10052

PR: https://git.openjdk.org/jdk/pull/10052