* [swift] Add bazel configuration for Swift
This change adds a simple bazel BUILD file for consuming the Swift
support. This also bumps the platforms bazel repo to fix support for M1s
and bazel 5.1+ https://github.com/bazelbuild/bazel/issues/15099#issuecomment-1075368289
The rules_swift inclusion here must happen before gRPC to ensure we
don't pull in an older version.
* Add CC=clang which is a requirement for Swift on Linux
* Add Swift to PATH
Keith Smiley