[googleapis_auth] Support impersonated_service_account in ADC #1359

Job	Run time
mono_repo self validate	22s
analyze_and_format; Dart dev; PKGS: _test, _test_package, discoveryapis_commons, discoveryapis_ge...	3m 51s
analyze_and_format; Dart 3.9.0; PKGS: _test, _test_package, discoveryapis_commons, discoveryapis_...	2m 17s
unittest; Dart 3.9.0; PKG: _test_package; `dart test`	29s
unittest; Dart 3.9.0; PKG: generated/googleapis; `dart test`	2m 33s
unittest; Dart 3.9.0; PKG: googleapis_auth; `dart test -p vm`	32s
unittest; Dart 3.9.0; PKG: discoveryapis_commons; `dart test`	30s
unittest; Dart 3.9.0; PKG: googleapis_auth; `dart test -p chrome --compiler dart2js,dart2wasm`	1m 51s
unittest; Dart dev; PKG: generated/googleapis; `dart test`	2m 41s
unittest; Dart dev; PKG: _test_package; `dart test`	28s
unittest; Dart dev; PKG: googleapis_auth; `dart test -p vm`	30s
unittest; Dart dev; PKG: generated/googleapis_beta; `dart test`	32s
unittest; Dart 3.9.0; PKG: discoveryapis_generator; `dart test`	32s
unittest; Dart 3.9.0; PKG: generated/googleapis_beta; `dart test`	46s
unittest; Dart dev; PKG: googleapis_auth; `dart test -p chrome --compiler dart2js,dart2wasm`	1m 40s
unittest; Dart dev; PKG: discoveryapis_commons; `dart test`	38s
unittest; Dart dev; PKG: discoveryapis_generator; `dart test`	41s
analyze_format; Dart 3.9.0; PKG: _googleapis_auth_e2e; `dart analyze`	23s
analyze_format; Dart dev; PKG: _googleapis_auth_e2e; `dart format --output=none --set-exit-if-cha...	21s
	21m 37s

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