Otherwise, the thread will continue to run and access the media data
buffer, which will have been freed.
The test here is a bit strange, but the issue would only consistently
repro after several GC runs.
With this change, we now have ~1200 CellAllocators across both LibJS and
LibWeb in a normal WebContent instance.
This gives us a minimum heap size of 4.7 MiB in the scenario where we
only have one cell allocated per type. Of course, in practice there will
be many more of each type, so the effective overhead is quite a bit
smaller than that in practice.
I left a few types unconverted to this mechanism because I got tired of
doing this. :^)
This function must return true if the object may intercept and customize
access to indexed properties (properties where the property name is a
non-negative integer.)
This will be used to implement fast path optimizations for array-like
accesses in subsequent commits.
