heap: Raise max backing store capacity for HeapVector

Align constant with PartitionAlloc, which uses something along the
lines of (1<<31)-X where X is some internal constant.

Oilpan doesn't have an implementation-imposed limit on the maximum
size of objects but rather can allocate until it runs OOM due to
either virtual cage exhaustion or actually running out of physical
memory.

Aligning the constant with PartitionAlloc allows for changing from
Vector to HeapVector and vice versa without side effects around
capacity.

Raising the corresponding limit in PA above something larger (than
fits into 32-bit signed integers) is a separate discussion to be held.

Change-Id: I842963c702640c3ba1680b82b339d4824bdfc2ad
Bug: chromium:1288561, chromium:1209303
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3447300
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Yuki Yamada <yukiy@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968823}