[third_party/pigweed] Roll 3 commits

b6d694586dbc0cd pw_unit_test: Add IWYU export/private pragmas
68ca4ccac262382 pw_bluetooth: Formatting fixes
e3662e8e52d2799 pw_kvs: Make Key an alias for string_view

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 463dca050a46608..b6d694586dbc0cd
Roller-URL: https://ci.chromium.org/b/8750271578590310865
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I40df65750e5de8017de45b515b6adf7541b4348f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/204690
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 463dca0..b6d6945 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 463dca050a46608077b3f556b25baaca11b0a48b
+Subproject commit b6d694586dbc0cde44c834e4d79f115611252af4