Switch `cronet_http` to use jnigen #772

Job	Run time
analyze_and_format; Dart 2.19.0; PKG: pkgs/http_client_conformance_tests; `dart analyze --fatal-i...	28s
mono_repo self validate	18s
analyze_and_format; Dart 3.0.0; PKG: pkgs/http; `dart analyze --fatal-infos`	36s
analyze_and_format; Dart dev; PKGS: pkgs/http, pkgs/http_client_conformance_tests; `dart analyze ...	35s
analyze_and_format; Dart dev; PKGS: pkgs/http, pkgs/http_client_conformance_tests; `dart format -...	25s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart test --platform vm`	55s
unit_test; Dart dev; PKG: pkgs/http; `dart run --define=no_default_http_client=true test/no_defau...	27s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart test --platform chrome`	2m 36s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart run --define=no_default_http_client=true test/no_def...	26s
unit_test; Dart dev; PKG: pkgs/http; `dart test --platform chrome`	2m 35s
unit_test; Dart dev; PKG: pkgs/http; `dart test --platform vm`	47s
	10m 8s

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