PR #2404: Add license header to all source files

Imported from GitHub PR https://github.com/google/nearby/pull/2404

Copybara import of the project:

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a6fbb3c396321c0b9012b787323f5f2ff652fd8f by Nick Bourdakos <bourdakos1@gmail.com>:

Add license header to all source files

Merging this change closes #2404

PiperOrigin-RevId: 623540004

fastpair/internal/impl/windows/BUILD

@@ -1,3 +1,17 @@
+# Copyright 2022 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 licenses(["notice"])
 
 cc_library(