Import wasi_cap_std_sync::Dir instead of wasi_cap_std_sync::dir::Dir.

[Berrysoft]

The former is re-exported from cap-std, which is the type used in preopen_dir, while the latter is the internal type of wasi_cap_std_sync. This change follows the behavior of wasmtime-wasi, and will reduce users' works on managing imports.

https://github.com/bytecodealliance/wasmtime/blob/main/crates/wasi/src/lib.rs#L15-L24

[paritytech-cicd-pr]

BENCHMARKS

	NATIVE			WASMTIME
BENCHMARK	MASTER	PR	DIFF	MASTER	PR	DIFF	WASMTIME OVERHEAD
execute/ bare_call_0	1.01ms	1.02ms	⚪ 1.20%	936.88µs	902.05µs	🟢 -3.65%	🟢 -12%
execute/ bare_call_0/typed	520.10µs	516.38µs	⚪ -0.94%	403.62µs	399.15µs	⚪ -0.99%	🟢 -23%
execute/ bare_call_1	1.05ms	1.06ms	🟢 0.56%	1.11ms	1.11ms	🟢 -0.41%	🟢 5%
execute/ bare_call_16	2.13ms	2.18ms	🟢 -0.80%	4.68ms	4.70ms	🟢 0.31%	🔴 116%
execute/ bare_call_16/typed	1.58ms	1.54ms	🟢 -2.42%	2.15ms	1.98ms	🟢 -8.23%	🟢 28%
execute/ bare_call_1/typed	603.22µs	608.90µs	⚪ 0.86%	713.28µs	688.56µs	🟢 -3.34%	🟢 13%
execute/ bare_call_4	1.19ms	1.19ms	🟢 0.05%	1.73ms	1.74ms	🟢 0.38%	🟢 46%
execute/ bare_call_4/typed	628.09µs	611.69µs	🟢 -2.69%	818.17µs	802.63µs	🟢 -1.88%	🟢 31%
execute/ br_table	633.96µs	641.18µs	⚪ -6.00%	910.42µs	880.44µs	🟢 -3.39%	🟢 37%
execute/ count_until	653.66µs	650.95µs	⚪ -0.86%	2.01ms	2.02ms	⚪ 0.24%	🔴 211%
execute/ factorial_iterative	303.45µs	365.29µs	🔴 20.60%	852.97µs	838.93µs	⚪ -1.06%	🔴 130%
execute/ factorial_recursive	605.01µs	610.84µs	⚪ 0.95%	1.26ms	1.34ms	🔴 6.87%	🔴 120%
execute/ fib_iterative	1.63ms	1.43ms	🟢 -12.43%	4.51ms	4.50ms	⚪ -0.15%	🔴 214%
execute/ fib_recursive	5.94ms	5.89ms	⚪ -0.96%	11.75ms	11.91ms	🔴 1.35%	🔴 102%
execute/ global_bump	948.63µs	948.29µs	⚪ -0.14%	3.13ms	3.14ms	⚪ 0.83%	🔴 231%
execute/ global_const	717.71µs	717.38µs	⚪ -0.17%	2.33ms	2.33ms	⚪ -0.22%	🔴 224%
execute/ host_calls	28.60µs	30.95µs	🔴 8.19%	37.54µs	37.64µs	⚪ 0.40%	🟢 22%
execute/ memory_fill	1.28ms	1.37ms	🔴 6.84%	3.91ms	3.90ms	⚪ -0.44%	🔴 185%
execute/ memory_sum	1.25ms	1.25ms	⚪ 0.04%	3.94ms	3.93ms	⚪ -0.03%	🔴 213%
execute/ memory_vec_add	2.82ms	2.59ms	🟢 -7.93%	8.26ms	8.31ms	⚪ 0.62%	🔴 221%
execute/ recursive_is_even	1.12ms	1.12ms	⚪ -0.26%	2.12ms	2.10ms	⚪ -1.11%	🟡 88%
execute/ recursive_ok	145.96µs	146.57µs	⚪ 0.63%	309.67µs	294.69µs	🟢 -4.84%	🔴 101%
execute/ recursive_scan	179.02µs	179.30µs	⚪ 0.26%	382.07µs	370.87µs	🟢 -2.80%	🔴 107%
execute/ recursive_trap	14.44µs	14.47µs	⚪ 0.31%	28.65µs	28.53µs	⚪ -0.67%	🟡 97%
execute/ regex_redux	543.07µs	545.28µs	⚪ 0.33%	1.40ms	1.40ms	⚪ 0.07%	🔴 156%
execute/ rev_complement	503.21µs	502.00µs	⚪ -0.18%	1.40ms	1.45ms	🔴 3.58%	🔴 189%
execute/ tiny_keccak	374.95µs	371.43µs	⚪ -1.16%	1.17ms	1.17ms	⚪ 0.00%	🔴 215%
execute/ trunc_f2i	917.85µs	909.56µs	⚪ -0.82%	2.38ms	2.38ms	⚪ 0.24%	🔴 162%
instantiate/ wasm_kernel	57.84µs	60.57µs	🔴 3.11%	94.96µs	65.96µs	🟢 -30.50%	🟢 9%
translate/ erc1155	205.63µs	208.65µs	🔴 1.52%	378.69µs	379.39µs	⚪ 0.24%	🟡 82%
translate/ erc20	101.31µs	102.63µs	🔴 1.32%	182.26µs	186.97µs	🔴 2.70%	🟡 82%
translate/ erc721	145.21µs	146.36µs	⚪ 0.84%	267.83µs	271.31µs	🔴 1.47%	🟡 85%
translate/ spidermonkey	0.00ns	0.00ns	⚪ -0.35%	0.00ns	0.00ns	⚪ 0.51%	🟢 0%
translate/ wasm_kernel	3.74ms	3.77ms	⚪ 0.93%	7.17ms	7.14ms	⚪ -0.45%	🟡 90%

Link to pipeline

[Robbepop]

Sorry I just missed this PR. Thanks!