ICU4X executors for 2.0 beta versions on datetime_fmt returns bad output for semantic skeletons

[sven-oly]

The executor in 20. beta1 doesn't handle semanticSkeleton or semanticSkeletonLength. Examples of output are below. Note that the second one returns "UKNOWN" for the label, which causes a crash in the validator part of the Conformance end-to-end process

These executors should properly handle the semantic skeleton input, and should not ever corrupt the input label for a test case.

            "error": "MismatchedTimeZoneFields",
            "error_type": "panic",
             {
            "error": "MismatchedTimeZoneFields",
            "error_type": "panic",
            "label": "016",
            "locale_label": "en"
        },
        {
            "label": "UNKNOWN",
            "input_data": "{\"locale\": \"en\", \"input_string\": \"2000-01-01T00:00:00Z\", \"options\": {\"timeZone\": \"Etc/GMT\", \"calendar\": \"gregory\"}, \"tz_offset_secs\": 0.0, \"label\": \"018\", \"original_input\": \"2000-01-01T00:00Z[Etc/GMT]\", \"skeleton\": \"yyMdEEE\", \"semanticSkeleton\": \"YMDE\", \"semanticSkeletonLength\": \"short\", \"hexhash\": \"e770078e197d2ac9d61abf1522b63d37fb7c5809\", \"test_type\": \"datetime_fmt\"}\n#EXIT\n",
            "error": "!!!! ERROR IN EXECUTION: 101. STDERR = thread 'main' panicked at src/../../common/../src/datetime_2_beta1.rs:118:26:\nunknown skeleton: YMDE\nstack backtrace:\n   0: rust_begin_unwind\n   1: core::panicking::panic_fmt\n   2: executor::run_all_tests::executors::datetimefmt::run_datetimeformat_test\n   3: executor::run_all_tests::main\nnote: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.\n"
        },       "label": "016",
            "locale_label": "en"
        },
        {
            "label": "UNKNOWN",
            "input_data": "{\"locale\": \"en\", \"input_string\": \"2000-01-01T00:00:00Z\", \"options\": {\"timeZone\": \"Etc/GMT\", \"calendar\": \"gregory\"}, \"tz_offset_secs\": 0.0, \"label\": \"018\", \"original_input\": \"2000-01-01T00:00Z[Etc/GMT]\", \"skeleton\": \"yyMdEEE\", \"semanticSkeleton\": \"YMDE\", \"semanticSkeletonLength\": \"short\", \"hexhash\": \"e770078e197d2ac9d61abf1522b63d37fb7c5809\", \"test_type\": \"datetime_fmt\"}\n#EXIT\n",
            "error": "!!!! ERROR IN EXECUTION: 101. STDERR = thread 'main' panicked at src/../../common/../src/datetime_2_beta1.rs:118:26:\nunknown skeleton: YMDE\nstack backtrace:\n   0: rust_begin_unwind\n   1: core::panicking::panic_fmt\n   2: executor::run_all_tests::executors::datetimefmt::run_datetimeformat_test\n   3: executor::run_all_tests::main\nnote: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.\n"
        },