Switch `cronet_http` to use jnigen #769

Job	Run time
analyze_and_format; Dart 2.19.0; PKG: pkgs/http_client_conformance_tests; `dart analyze --fatal-i...	39s
analyze_and_format; Dart 3.0.0; PKG: pkgs/http; `dart analyze --fatal-infos`	24s
mono_repo self validate	19s
analyze_and_format; Dart dev; PKGS: pkgs/http, pkgs/http_client_conformance_tests; `dart analyze ...	41s
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 run --define=no_default_http_client=true test/no_def...	32s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart test --platform chrome`	2m 23s
unit_test; Dart dev; PKG: pkgs/http; `dart run --define=no_default_http_client=true test/no_defau...	20s
unit_test; Dart dev; PKG: pkgs/http; `dart test --platform chrome`	3m 19s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart test --platform vm`	46s
unit_test; Dart dev; PKG: pkgs/http; `dart test --platform vm`	54s
	10m 42s

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