[roll third_party/pigweed] pw_cpu_exception_cortex_m: Correct namespaces

Also adds re-use of the existing constants for the entry test.

Also renames the pw.cpu_exception.cortex_m.SnapshotCpuState
to be SnapshotCpuStateOverlay to differentiate from the function
and to explicitly describe what this snapshot proto message is.

Original-Requires: pigweed-internal:19840
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/74600

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: ea719194a262698..b402c558ea6c269
Roller-URL: https://ci.chromium.org/b/8827105919060720257
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827105919060720257
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Icbec36df13a97739ddc0fcffae35dd995638db9f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/76200
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 ea71919..b402c55 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ea719194a262698b1e3383d9e0a4c71f6ea0efbc
+Subproject commit b402c558ea6c2698559ffcd34ff4246eec55a04f