Move sdk executor_runner to sdk/fb/runners folder to hide from OSS with hg mv

Summary:
Move sdk executor_runner to sdk/fb/runners folder to hide from OSS.

[1/n] in a series of diffs to consoldate/organize the various copies of executor_runner in the OSS executorch repo

Very simple change:
1. move `sdk/runners` folder under `sdk/fb/runners` using `hg mv`
2. biggrep for `executorch/sdk/runners`, replace with `executorch/sdk/fb/runners`

Differential Revision: D49929099

Author: Varun Puri

docs/website/docs/tutorials/bundled_program.md

@@ -128,7 +128,7 @@ __ET_NODISCARD Error VerifyResultWithBundledExpectedOutput(
 
 ### Example
 
-Here we provide an example about how to run the bundled program step by step. Most of the code are borrowed from "fbcode/executorch/sdk/runners/executor_runner.cpp" and please review that file if you need more info and context:
+Here we provide an example about how to run the bundled program step by step. Most of the code are borrowed from "fbcode/executorch/sdk/fb/runners/executor_runner.cpp" and please review that file if you need more info and context:
 
 ```c++
     // method_name is the name for the method we want to test

runtime/executor/test/targets.bzl

@@ -18,7 +18,7 @@ def define_common_targets(is_fbcode = False):
                 "//executorch/exir/backend/test/...",
                 "//executorch/runtime/backend/...",
                 "//executorch/extension/pybindings/...",
-                "//executorch/sdk/runners/...",
+                "//executorch/sdk/fb/runners/...",
                 "//executorch/test/...",
                 "//executorch/examples/...",
             ],
@@ -42,7 +42,7 @@ def define_common_targets(is_fbcode = False):
                 "//executorch/exir/backend/test/...",
                 "//executorch/runtime/backend/...",
                 "//executorch/extension/pybindings/...",
-                "//executorch/sdk/runners/...",
+                "//executorch/sdk/fb/runners/...",
                 "//executorch/test/...",
                 "//executorch/examples/...",
             ],

sdk/runners/TARGETS renamed to sdk/fb/runners/TARGETS

@@ -1,10 +1,4 @@
-/*
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree.
- */
+// (c) Meta Platforms, Inc. and affiliates. Confidential and proprietary.
 
 #include <gflags/gflags.h>