chore: update copyright header to Google LLC BSD format #1350

Job	Run time
mono_repo self validate	28s
analyze_and_format; Dart dev; PKGS: _test, _test_package, discoveryapis_commons, discoveryapis_ge...	4m 13s
analyze_and_format; Dart 3.9.0; PKGS: _test, _test_package, discoveryapis_commons, discoveryapis_...	2m 16s
unittest; Dart 3.9.0; PKG: discoveryapis_generator; `dart test`	31s
unittest; Dart 3.9.0; PKG: discoveryapis_commons; `dart test`	44s
unittest; Dart 3.9.0; PKG: _test_package; `dart test`	41s
unittest; Dart 3.9.0; PKG: generated/googleapis_beta; `dart test`	36s
unittest; Dart 3.9.0; PKG: googleapis_auth; `dart test -p chrome --compiler dart2js,dart2wasm`	1m 39s
unittest; Dart dev; PKG: googleapis_auth; `dart test -p chrome --compiler dart2js,dart2wasm`	1m 47s
unittest; Dart dev; PKG: _test_package; `dart test`	38s
unittest; Dart 3.9.0; PKG: googleapis_auth; `dart test -p vm`	45s
unittest; Dart dev; PKG: googleapis_auth; `dart test -p vm`	29s
unittest; Dart dev; PKG: discoveryapis_commons; `dart test`	43s
unittest; Dart dev; PKG: discoveryapis_generator; `dart test`	45s
unittest; Dart dev; PKG: generated/googleapis_beta; `dart test`	44s
unittest; Dart dev; PKG: generated/googleapis; `dart test`	2m 35s
unittest; Dart 3.9.0; PKG: generated/googleapis; `dart test`	2m 33s
analyze_format; Dart 3.9.0; PKG: _googleapis_auth_e2e; `dart analyze`	34s
analyze_format; Dart dev; PKG: _googleapis_auth_e2e; `dart format --output=none --set-exit-if-cha...	35s
	23m 16s

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