RFR: 8351087: Combine scratch object tables in heapShared.cpp

[Calvin Cheung]

On Mon, 3 Mar 2025 21:50:38 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> Please review this trivial change. The two tables `_scratch_java_mirror_table` and `_scratch_references_table` are always disjoint. So we can simply combine them into a single table.
> 
> I am running tiers 1-5 for sanity sake.

LGTM

-------------

Marked as reviewed by ccheung (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23876#pullrequestreview-2655514511