If V8_SHARED_RO_HEAP is set, then GetSharedMemoryStatistics now reports
the size of RO_SPACE. Additionally size values for RO_SPACE are zeroed
in the per-isolate Heap and Space stats.

Bug: v8:7464
Change-Id: I2d6843c001b55974460d1df034f08d1ed5b0d8da
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1900459
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65231}