Reland "Merge commit '4c51abf12053e3c43a62059c693322ea992b35ce' into main"

This is a reland of commit 98137ddf9a4ca85fcf18ab1b4923fcf46e38748d

It is not tenable to have to fully patch fuchsia.git's //build/secondary/third_party/grpc/BUILD.gn into the main here whenever we need to update the gRPC GI pin and avoid a breaking change so instead we have decided to maintain the copy here in sync with //build/secondary/third_party/grpc/BUILD.gn

Original change's description:
> Merge commit '4c51abf12053e3c43a62059c693322ea992b35ce' into main
>
> Removed Fuchsia specific local patch: templates/BUILD.gn.template and README.Fuchsia
>
> Copied BUILD.gn from https://fuchsia-review.git.corp.google.com/c/fuchsia/+/1151492
>
> https://fuchsia.googlesource.com/third_party/grpc/+/4c51abf12053e3c43a62059c693322ea992b35ce is the head commit of tag/1.48.0-pre1
> Run git diff between this commit and 4c51abf12053e3c43a62059c693322ea992b35ce, the only diff is BUILD.gn.
>
> Note that this change is ONLY used for avoiding breaking change. It is a transition change for upreving gRPC to tag/1.48.0-pre1.
>
> Bug: 377536116
>
> Change-Id: Ie4eefa0f9c2abecf051a856bd885fb6f905b0144
> Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/grpc/+/1151415
> Reviewed-by: Francois Rousseau <frousseau@google.com>

Bug: 377536116
Change-Id: I61e5ac7fede996f9334ee6b397bb086d56cbc00b
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/grpc/+/1157254
Reviewed-by: Francois Rousseau <frousseau@google.com>