Add rust macros in new location

Summary:
D80827538 changed Rust macro imports from `fbcode_macros//build_defs:rust_{library,binary,unittest}.bzl` to `fbsource//tools/build_defs:rust_{library,binary,unittest}.bzl` and the old location is being imminently deleted.

Facebook open-source projects map both `fbcode_macros` and `fbsource` to this fbcode/github/standard/shim directory. So we need some new files under shim/tools/build_defs/rust_{}.bzl that mirror the existing shim/build_defs/rust_{}.bzl.

https://www.internalfb.com/code/fbsource/[6e8ef076aafbe4d8b2726a250ae137f219b0481e]/fbcode/github/standard/shim/.buckconfig.d/common.buckconfig?lines=5%2C11-12

https://www.internalfb.com/code/fbsource/[6e8ef076aafbe4d8b2726a250ae137f219b0481e]/fbcode/buck2/oss/.buckconfig?lines=1%2C3

Reviewed By: cjlongoria

Differential Revision:
D81150005

Privacy Context Container: L1292898

fbshipit-source-id: be65d496c9d475eabb9e8f8826859e33883b351e

Author: David Tolnay

shim/tools/build_defs/rust_binary.bzl

@@ -0,0 +1,11 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is dual-licensed under either the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree or the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree. You may select, at your option, one of the
+# above-listed licenses.
+
+load("@shim//:shims.bzl", _rust_binary = "rust_binary")
+
+rust_binary = _rust_binary

shim/tools/build_defs/rust_library.bzl

@@ -0,0 +1,11 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is dual-licensed under either the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree or the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree. You may select, at your option, one of the
+# above-listed licenses.
+
+load("@shim//:shims.bzl", _rust_library = "rust_library")
+
+rust_library = _rust_library

shim/tools/build_defs/rust_unittest.bzl

@@ -0,0 +1,11 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is dual-licensed under either the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree or the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree. You may select, at your option, one of the
+# above-listed licenses.
+
+load("@shim//:shims.bzl", _rust_unittest = "rust_unittest")
+
+rust_unittest = _rust_unittest