[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/8827924880203226769
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827924880203226769
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I984353da0af2e93c50942d5c79d477bc4668d434
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/73980
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