[roll third_party/pigweed] pw_async2: Add AllocateTask

This function makes it easy to have a runtime-allocated task which will
be deallocated upon completion.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/206812
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https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 8c5103f3da47d9c..58a09c188df0cc6
Roller-URL: https://ci.chromium.org/b/8749095395098576241
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I1729e33c18dba2e7ced085786bd576c79c468e82
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/207582
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
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Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 8c5103f..58a09c1 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 8c5103f3da47d9c02e9d66f57ce6a71b1fadce32
+Subproject commit 58a09c188df0cc663a295874e51587352585333b