RFR: 8279063: Consolidate push and push_if_necessary in PreservedMarks

[Albert Mingkun Yang]

On Tue, 21 Dec 2021 13:27:46 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple change of cleaning up `PreservedMarks` API.
> 
> Test: hotspot_gc

Thanks for the review.

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PR: https://git.openjdk.java.net/jdk/pull/6909