RFR: 8065760: CHA: Improve abstract method support

[Tobias Hartmann]

On Wed, 26 May 2021 20:59:03 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> 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

Looks good to me too.

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Marked as reviewed by thartmann (Reviewer).

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