Reland "partition_alloc: Move pa tests into pa."

This reverts commit 5d5831911b0bbd0053b470cf4cf7528c1f71c3be.

The diff is fixing an issue on Android.

On Android the 'open' function has two versions:
- int open(const char *pathname, int flags);
- int open(const char *pathname, int flags, mode_t mode);

This doesn't play well with WrapEINTR template. So an alias
was created

Original change's description:
> Revert "partition_alloc: Move pa tests into pa."
>
> This reverts commit 17884376ce344ef4a926f22beb621801e8236c7c.
>
> Reason for revert: Fails to compile on `android-archive-rel`
> https://ci.chromium.org/ui/p/chromium/builders/ci/android-archive-rel/42067/overview
>
> NOTRY=true
> NOTREECHECKS=true
>
> Original change's description:
> > partition_alloc: Move pa tests into pa.
> >
> > This addresses a TODO about moving partition_alloc's tests into
> > partition_alloc.
> >
> > Bug: 40158212
> > Change-Id: Ia4b2017e2da38bd3fed904558126076b2deafc51
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5659601
> > Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
> > Reviewed-by: Kentaro Hara <haraken@chromium.org>
> > Reviewed-by: danakj <danakj@chromium.org>
> > Reviewed-by: Colin Blundell <blundell@chromium.org>
> > Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1323243}
>
> Bug: 40158212
> Change-Id: I8831dbcffd8c328a0722fe1f53e382c68a6056a9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5676232
> Commit-Queue: Titouan Rigoudy <titouan@chromium.org>
> Auto-Submit: Titouan Rigoudy <titouan@chromium.org>
> Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
> Owners-Override: Titouan Rigoudy <titouan@chromium.org>
> Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#1323249}

Bug: 40158212
Change-Id: Ie60a85c296224ef3cfdcc17371db100cf2ce0db1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5675456
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1323319}
NOKEYCHECK=True
GitOrigin-RevId: 2ecbb28535ff5b11e4cab16680b84d29c0afe039
11 files changed