[roll third_party/pigweed] pw_analog: Add MicrovoltInput class

Add interface for converting an analog sample into a fixed point
voltage in microvolts with MicrovoltInput.

Testing:
Host test -- OK

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/43840

third_party/pigweed Rolled-Commits: 55bb0ad51bb7c47..c24e33273f1e5ae
Roller-URL: https://ci.chromium.org/b/8846128675629413344
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8846128675629413344
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: If1a74dac51b87f5b7823023b4eb3e4105ea89148
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/47241
Reviewed-by: 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 55bb0ad..c24e332 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 55bb0ad51bb7c47f937eed5944df1a42ffc12c6e
+Subproject commit c24e33273f1e5ae2f68b880d08e1928a9737d7b6