[roll third_party/pigweed] pw_log_string: Enable HandleMessage configurability

Updates pw_log_string's handler to use an optionable and configurable
PW_LOG_STRING_HANDLE_MESSAGE macro which invokes
pw_log_string_Handle_message.

The pw_log_string backend for pw_log is updated accordingly to use this
configurable macro to permit users to customize what arguments are
passed to the actual handler backend.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/149131

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: c359686b4a32ba9..da7dc2855398dfb
Roller-URL: https://ci.chromium.org/b/8779562773975757937
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I3883043c7f9877ea70707f8a1563719c597f1d7f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/149731
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 c359686..da7dc28 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c359686b4a32ba99d227ee4d3650119b0084b906
+Subproject commit da7dc2855398dfb6b1dc111eef8b152479952c97