RFR: 8293315: Add back logging for Placeholders

[Ioi Lam]

On Fri, 2 Sep 2022 14:23:22 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> I lost some information in the logging code for PlaceholderTable that I really want when I converted it to use a ResourceHashtable, so this minor patch adds it back.
> Tested locally with -Xlog:class+load+placeholders=trace, and tier1.

Looks good and trivial.

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Marked as reviewed by iklam (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10145