roll: third_party/pigweed pw_bluetooth_sapphire: Separate gtest deps from test libs

Many of the bt-host unit tests depend on aspects of gtest and gmock that
are not supported by //pw_unit_test:light. These dependencies were
picked up primarily via //pw_bluetooth_sapphire:test_helpers.

This CL moves the gtest specific portions to a new "gtest_helpers"
target, making it easier to centralize the compatibility check and to
create test-related code, such as fuzzers, that do not depend on gtest.

Original-Bug: 352808542
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/253833
Original-Revision: 72d815eed764e4a8f60aca07217d18d6ab59155c

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: ce6f2c33b4f0b6..72d815eed764e4
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8726154508528482177
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I278513751ebdf9b11f37cf3cc10a183ba318a305
Reviewed-on: https://pigweed-review.googlesource.com/c/gonk/+/259552
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index ce6f2c3..72d815e 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ce6f2c33b4f0b6d65f843e3de18e21dae1ca0f1f
+Subproject commit 72d815eed764e4a8f60aca07217d18d6ab59155c