RFR: 8065760: CHA: Improve abstract method support

[Vladimir Ivanov]

Enable CHA to look for unique concrete methods under abstract root methods.
Only vtable-based implementation is affected. Old implementation is left as is.

The unit test requires #4211 and #4212 to pass.

Testing:
- [x] hs-tier1 - hs-tier9

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Commit messages:
 - Test case
 - Enable abstract root method support

Changes: https://git.openjdk.java.net/jdk/pull/4213/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4213&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8065760
  Stats: 901 lines in 6 files changed: 543 ins; 307 del; 51 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4213.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4213/head:pull/4213

PR: https://git.openjdk.java.net/jdk/pull/4213