[roll third_party/pigweed] docs: Use Furo Sphinx theme

- Switch Sphinx theme to https://github.com/pradyunsg/furo
- Apply some custom colors
- Add css styling for audodoc signatures similar to default
  sphinx_rtd_theme
- Remove .. contents:: :local: blocks since this theme has
  a right side local table of contents.
- New pigweed-code-light Pygments theme for use in the
  pw_console and the docs website. Syntax highlighting for
  both matches now.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/57064

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 7f2f4f1f90f386e..9130758cd71e4cf
Roller-URL: https://ci.chromium.org/b/8838729686918784544
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8838729686918784544
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I0babdc36838597aa369c7bed8c9a34b18f933c95
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/57302
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 7f2f4f1..9130758 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7f2f4f1f90f386e0b959485154f26b0be85fc040
+Subproject commit 9130758cd71e4cf081395835cfbf685bc0bf069c