RFR: 8292286: Convert PlaceholderTable to ResourceHashtable [v3]

[Coleen Phillimore]

On Mon, 15 Aug 2022 18:19:41 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This change converts the PlaceholderTable to ResourceHashtable.  It's much like the ResolutionErrorTable conversion.  This change has been performance tested with the previous set of testing with no regression.  It's also been tested tier1-3 and 4-7 with the other tables in my patch queue.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Ioi comments.

Thank you Harold and Ioi for the code reviews.  I filed RFE JDK-8292383 to make the refcounting for ResourceHashtables key less error prone and this table will change for that too.

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PR: https://git.openjdk.org/jdk/pull/9854