roll: pigweed pw_allocator: Avoid read of invalid requested size

Prior to this CL, block types which included the `BlockWithLayout`
mix-in would read the previous requested size in `DoResize`. That method
would be called as part of `Alignable::DoAllocAligned` before a
requested size had been set.

This CL also resets the padding of a detailed block to 0 on free. This
ensures the padding can never exceed the block size on allocation.

Original-Bug: 446769988
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/326312
Original-Revision: b00699103392091fa54e4b6619faa6e2200e2e6c

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: 8257af2f61c7cf..b0069910339209
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8702427457689305985
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I7cf853c29dd096f024838d881bb2e29f672d2fad
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/showcase/sense/+/326833
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
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