[roll third_party/pigweed] pw_string: Use size_t in interface

pw_string uses `pw::string_inpl::size_type`, which is `unsigned short`,
to store string sizes. Unfortunately a quirk that C++ inherits from C is
that unsigned types smaller than `int` are promoted to *signed* `int`s.

pw_string currently works around this by making frequent static_casts,
but this approach breaks down when trying to use `pw::InlineString` with
third-party code that expects to work with "string-like" types. For
example, FuzzTest tries to compare string sizes to other `size_t`s and
fails to build.

With this CL, `InlineString` still uses `size_type` for storage, but
takes and returns size values of `size_t`.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/148332

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: f77c77808bab4a0..f22bfc338782fbf
Roller-URL: https://ci.chromium.org/b/8779837453623290177
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I51715100f8e9e18fd4460703d63c7647fe6593b0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/149271
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 f77c778..f22bfc3 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit f77c77808bab4a0ec60836b8d9470382252f013d
+Subproject commit f22bfc338782fbf7ac05c6f9b3f5d7ac8c415097