Reland "Split PartitionAlloc headers into internal ones and public ones"

This is reland of crrev.com/c/7795856. The reason why 7795856 was
reverted is that allocator_shim_default_dispatch_to_partition_alloc.cc
depends on address_pool_manager.h directly, but doesn't include it
(indirectly include). So modified
allocator_shim_default_dispatch_to_partition_alloc.cc to include it.

The reason why No-Try is that linux-chromeos-rel's ash_unittests fail
because of timeout. The timeouts seemed to be caused by llvm_profiler
(code coverage check). If this CL causes the same timeouts after
landing, I will revert this CL.

Bypass-Check-License: page_allocator_internal.h is just moved, not newly added. No need to check its license.
No-Try: true
Change-Id: I3c21220d90956210110095e70d6ea74931cbddd4
Cq-Include-Trybots: luci.chromium.try:android-cast-arm-rel,android-cast-arm64-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7847692
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Reviewed-by: Giovanni Ortuno Urquidi <ortuno@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/main@{#1630913}
NOKEYCHECK=True
GitOrigin-RevId: 7c766eb88a59f73ca3cdf80f4e1bd4ef992ed310