[roll third_party/pigweed] pw_string: Add insert, erase

Original-Bug: b/239996007
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/148333

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 255ab6106000d8d..0afc2d5743f9af7
Roller-URL: https://ci.chromium.org/b/8779654577504495649
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I70df988a75cad5b810d0e0488897d221a736e05a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/149454
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 255ab61..0afc2d5 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 255ab6106000d8d698ed61105bb40b11eecdaf6e
+Subproject commit 0afc2d5743f9af77d5c8007f5b8720370b3e3ac9