roll: third_party/pigweed Reland "docs: Enable Doxylink"

This is a reland of commit ed98e925da046f4ecfe802e890efb0258253f256

https://pwrev.dev/299993 was reverted because the local macOS ARM docs
build was failing. As of https://pwrev.dev/309760 that tryjob coverage
gap is now filled. The root issue was the hardcoded tagfile path in
//docs/doxygen/Doxyfile that change #299993 introduced. This hardcoded
path is invalid on macOS ARM. The new OUTDIR feature introduced in
https://github.com/TendTo/rules_doxygen/pull/30 lets us configure this
path properly for all host OSes.

Original-Bug: 434937497

Original change's description:
> docs: Enable Doxylink
>
> Doxylink is a lightweight Sphinx extension that makes it easy
> to link from the main pigweed.dev site (powered by Sphinx)
> to the pigweed.dev/doxygen subsite (powered by Doxygen).
>
> Original-Bug: 426012010
>
> Change-Id: I49c6c66a8bbb45dc05a47df0e526a5d5acf5a5a3
> Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/299993
> Pigweed-Auto-Submit: Kayce Basques <kayce@google.com>
> Tests-Not-Needed: Kayce Basques <kayce@google.com>
> Copybara-Verified: Copybara Prod <copybara-worker-blackhole@google.com>
> Commit-Queue: Kayce Basques <kayce@google.com>
> Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
> Reviewed-by: Armando Montanez <amontanez@google.com>

Original-Bug: 426012010
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/309434
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: 494717f520908dc9d351dc612b9741270d3f117d

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: 4bdcd99f0c0c75..494717f520908d
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8707412130241585137
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I44e9630421442552c972c60f64282552fe871fb5
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/310655
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.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 4bdcd99..494717f 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4bdcd99f0c0c754c4aba19928a7192a393df7c74
+Subproject commit 494717f520908dc9d351dc612b9741270d3f117d