[roll third_party/pigweed] pw_allocator: Move Layout and UniquePtr to their own header files

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/199534

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 4f049a2e95df9ca..30f64d3eedfbd31
Roller-URL: https://ci.chromium.org/b/8751755959513971313
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iab767a5ef92456a27462b664ed1b92febde5d678
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/201510
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 4f049a2..30f64d3 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4f049a2e95df9caaad1cf37b4e8104a3f79fc81c
+Subproject commit 30f64d3eedfbd313d62d0a50c1ef6bfdbd514182