[roll third_party/pigweed] pw_software_udpate: Reland manifest writing

Since we decided to keep the manifest targets metadata map, the original
implementation and test code that were removed in http://pwrev/67082 can
now be added back.

Original-Bug: 456
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/67344

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: b5fa5d338236851..3f758de82ca98a9
Roller-URL: https://ci.chromium.org/b/8827924880925340497
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8827924880925340497
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I63d6c1a35c4c0c17ca9a1be98be47c2eec6db819
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/73981
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index b5fa5d3..3f758de 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b5fa5d3382368516cf8a11204371c0cde4eb8bd4
+Subproject commit 3f758de82ca98a92e6bfc3899a233a179a66fe63