[rust] Switch serde_jsonrc -> serde_json_lenient.

Formerly we used serde_jsonrc, a Rust JSON parser which accepts some
format extensions. With this CL we switch to serde_json_lenient which is
similar but more up to date with the upstream (strict) JSON parser
serde_json.

This is necessary so that we can get the benefit of the float_roundtrip
mode recently introduced upstream.

Beyond that, there are no intentional functional changes.

This change appears large because previously, serde_jsonrc was pulled in
via a DEPS entry. With this change, we vendor it into place like the
rest of our crates. Hence, there are many "new" files though they are
all largely identical to the serde_jsonrc which we previously pulled in
via DEPS.

A full diff of the changes can be seen via:
https://github.com/google/serde_json_lenient/compare/ca5782632fc8dc3f9cf2f22055b87f910cad761f..01d0cf01520d3c5be23825ec979998fb80c780e6
most of which is due to upgrading to a more recent underlying
serde_json.

Bug: 1301719
Change-Id: If43f9f3900125c92cac9cbbc3749d31cb3085a3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3511416
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@google.com>
Commit-Queue: Adrian Taylor <adetaylor@chromium.org>
Cr-Commit-Position: refs/heads/main@{#981383}