RFR: 8257020: [JVMCI] enable a JVMCICompiler to specify which GCs it supports

[Doug Simon]

A number of jtreg tests require a specific GC. These tests should be ignored when EnableJVMCI is true and the JVMCI compiler does not support the required GC.

This PR adds `JVMCICompiler.isGCSupported` and makes use of it in `WhiteBox.isGCSupported`.

Prior to this PR, a test requiring a GC not yet supported by a JVMCI compiler fail as follows:
Error occurred during initialization of VM
JVMCI Compiler does not support selected GC: epsilon gc

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Commit messages:
 - move logic to GCConfig
 - enable a JVMCICompiler to specify which GCs it supports

Changes: https://git.openjdk.java.net/jdk/pull/1423/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1423&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257020
  Stats: 107 lines in 12 files changed: 91 ins; 15 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1423.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1423/head:pull/1423

PR: https://git.openjdk.java.net/jdk/pull/1423