RFR: 8036580: CHA: improve default method support

[Nils Eliasson]

On Wed, 26 May 2021 22:48:15 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> Enable CHA to look for unique concrete methods under default interface methods.
> Only vtable-based implementation is affected. Old implementation is left as is.
> 
> The unit test requires #4211/#4212 to pass and relies on test code refactorings from #4213.
> 
> Testing:
> - [x] hs-tier1 - hs-tier9

Looks good.

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Marked as reviewed by neliasso (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4214