[snapshot] Check CanDiscardCompiled() again before DiscardCompiled()

Since DiscardCompiled() can allocate, it could also a cause a GC. A full
GC might perform bytecode flushing, which could change the return value
of CanDiscardCompiled(). So a DiscardCompiled() invocation in one loop
iteration could violate the assumption that CanDiscardCompiled() holds
in subsequent iterations. Prevent DCHECK failure by checking whether
CanDiscardCompiled() still holds for each SharedFunctionInfo.

Bug: v8:11772
Change-Id: Ie9c704abeea801bd3f4f1bdf8fa9c51a8a9d447d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2960274


Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75178}