[roll] Roll fuchsia [bindgen] Integrate bindgen into the build system

Now that bindgen is statically linked to libclang, we can integrate it
into the build system. This patch uses the golden-files pattern to allow
for bindgen-generated code to be checked-in for review, and validation
at compile time to make sure the checked-in code matches the generated
code. It then migrates some of internal users of an external bindgen
over to use it.

The script is temporarily named new-bindgen.py until we finish migrating
all the current users of the `bindgen.sh` scripts, or using the
`generate.py` patterns.

This migrates`sdk/lib/async/rust/sys` as the first version, with other
migrations done in future patches.

Original-Original-Bug: 42159024
Original-Original-Bug: 42153476
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1644774
Original-Original-Revision: 8d809d577c0806db584c62200924bb1855778440
GitOrigin-RevId: 727a6afa02ea81b96f41d57e8adc4792e7daed4b
Change-Id: Iac45061b07534b2e2dd387c4bc31becfeb39fd33
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1653652
Cr-Commit-Position: refs/heads/main@{#194720}