[roll third_party/pigweed] pw_sync: add class InlineBorrowable

InlineBorrowable owns an object and a mutex that guards the object.
Both the object and mutex are constructed in-place, and the object can
only be accessed by calling acquire() or one of the acquire_*() methods.

InlineBorrowable should be used whenever an object needs to be guarded
for its entire lifetime by a single mutex. InlineBorrowable extends
Borrowable, so it can be passed to existing APIs by reference.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/103180

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 25b197a80c5d3fa..67e71ad7f7a3e8d
Roller-URL: https://ci.chromium.org/b/8802832193733744865
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I4d9d27e2412cdcc5aea105337c29261b0805a413
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/110705
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 25b197a..67e71ad 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 25b197a80c5d3fa87f46c67f67e625a6d23a899b
+Subproject commit 67e71ad7f7a3e8dfc63799d8ff241cd0a6daf9ee