[strong] Add test for strong load involving proxies
[strong] Add test for strong load involving proxies

Keeping this CL separate in case there are more GC-stress problems.

BUG=v8:3956
LOG=N

Review URL: https://codereview.chromium.org/1217543006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29449}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh