[roll] Roll fuchsia [fidl][cpp] Make fidl::Client thread/sequence affine

{fidl,fdf}::{Wire}Client has the following semantics:
- You must bind it and destroy it on the same dispatcher
- The dispatcher must be single-threaded/synchronized
- You could make FIDL calls from arbitrary threads

The last bullet point is surprising: given a client
running on thread A, one could make a FIDL call from
thread B, but the response callback is still invoked from
thread A.

This behavior is especially surprising in the context of driver
dispatchers: a driver on dispatcher B could make a call on a client
running on dispatcher A. Then the driver B will later get called from
the wrong dispatcher, messing up internal state.

Fortunately it appears nothing on the system does these
cross-thread/cross-dispatcher calls on WireClient/Client. It seems
simpler to completely take out any multi-threading feature from the
non-shared clients.

After this CL, fidl::{Wire}Client has the following semantics:
- You must bind it and destroy it on the same dispatcher
- The dispatcher must be single-threaded
- You must make FIDL calls from the dispatcher thread

After this CL, fdf::{Wire}Client has the following semantics:
- You must bind it and destroy it on the same dispatcher
- The dispatcher must be synchronized
- You must make FIDL calls from tasks run on that synchronized
  dispatcher

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/706828
Original-Revision: 2cb2c809fcb654ff861d5b838b7c548cf300fa21
GitOrigin-RevId: a64cad57b821222a5643e646f2a8d4c2785e518f
Change-Id: I464b163251040e86f85628eacacb36e000c41a25