Fix up generated header include paths
Fix up generated header include paths

The "hello_sapi" example lives in a different WORKSPACE as it is intended to
show how to embed SAPI in your own projects. However, this is not compatible
with simply running `bazel build //sandboxed_api/...` after checkout.

This change simply replace `copts = ["-I."]` with `includes = ["."]`, so that
generated headers can be found reliably, regardless of how the example is
compiled.

PiperOrigin-RevId: 313782756
Change-Id: Iac26e828146b01545c81d9500f5f68fa0f2d4ddf

google/sandboxed-api,google/sandboxed-api,google/sandboxed-api,google/sandboxed-api