chore: add downloadData and downloadFile e2e tests #2567

Job	Run time
test / test-dart-vm (3.0.1)	2m 26s
test / test-dart-vm (stable)	2m 52s
dart2js_test / test-dart-2js (3.0.1, chrome)	4m 32s
dart2js_test / test-dart-2js (3.0.1, firefox)	4m 45s
ddc_test / test-dart-ddc (3.0.1, chrome)	4m 3s
dart2js_test / test-dart-2js (stable, chrome)	4m 4s
ddc_test / test-dart-ddc (3.0.1, firefox)	4m 22s
dart2js_test / test-dart-2js (stable, firefox)	4m 26s
ddc_test / test-dart-ddc (stable, chrome)	3m 48s
ddc_test / test-dart-ddc (stable, firefox)	4m 14s
native_test / test-dart-native (macos-latest)	2m 54s
native_test / test-dart-native (windows-latest)	3m 17s
	45m 43s

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