[bazel][ci] Add CI action to generate pregen patch (#8816)

There were complaints about no patch files being created from CI when
the examples pre-gen fails for people who don't build with bazel. This
adds a new action step to run just the non-robotpy pregen.

I also added an argument to the diff tests to make it a unified diff,
which might make it easier to hand fix.

shared/bazel/rules/robotpy/build_info_gen.bzl

@@ -34,6 +34,7 @@ def generate_robotpy_native_wrapper_build_info(name, pyproject_toml, third_party
         suggested_update_target = "//:write_robotpy_generated_native_files",
         tags = ["robotpy"],
         target_compatible_with = robotpy_compatibility_select(),
+        diff_args = ["-u"],
     )
 
 def generate_robotpy_pybind_build_info(
@@ -91,4 +92,5 @@ def generate_robotpy_pybind_build_info(
         visibility = ["//visibility:public"],
         tags = ["robotpy"],
         target_compatible_with = robotpy_compatibility_select(),
+        diff_args = ["-u"],
     )

shared/bazel/rules/robotpy/semiwrap_tool_helpers.bzl

@@ -61,6 +61,7 @@ def update_yaml_files(name, yaml_output_directory = "src/main/python/semiwrap",
         suggested_update_target = "//:write_all",
         target_compatible_with = robotpy_compatibility_select(),
         visibility = ["//visibility:public"],
+        diff_args = ["-u"],
     )
 
 def scan_headers(name, pyproject_toml, package_root_file, extra_hdrs, pkgcfgs):