Default ExecuTorch targets to ExecuTorch-wide Buck visibility (pytorch#8969)

IMO, Buck visibility is just inverse deps. We should trust that people have a good reason to add deps rather than attempt to police them and require double entry in both deps and visibility, especially since we seem to be committed to APIs by default in OSS anyway.

Specific motivation is that pytorch#8712 would otherwise have to ad-hoc slap ExecuTorch-wide visibility on a lot of targets, but I've held this view for a long time.

Differential Revision: D70647462

Author: swolchok

shim_et/xplat/executorch/build/runtime_wrapper.bzl

@@ -187,6 +187,9 @@ def _patch_kwargs_common(kwargs):
     for dep_type in ("deps", "exported_deps"):
         env.patch_deps(kwargs, dep_type)
 
+    if "visibility" not in kwargs:
+        kwargs["visibility"] = ["//executorch/..."]
+
     # Patch up references to "//executorch/..." in lists of build targets,
     # if necessary.
     use_static_deps = kwargs.pop("use_static_deps", False)
@@ -202,10 +205,6 @@ def _patch_kwargs_common(kwargs):
                 function = native.partial(_patch_executorch_references, use_static_deps = use_static_deps),
             )
 
-    # Make all targets private by default, like in xplat.
-    if "visibility" not in kwargs:
-        kwargs["visibility"] = []
-
     # If we see certain strings in the "visibility" list, expand them.
     if "@EXECUTORCH_CLIENTS" in kwargs["visibility"]:
         # See env.executorch_clients for this list.