Make Module::imports iterator return FuncType instead of DedupFuncType

[Robbepop]

From what I understand about the sparse description of the issue this PR closes #581.

[paritytech-cicd-pr]

BENCHMARKS

	NATIVE			WASMTIME
BENCHMARK	MASTER	PR	DIFF	MASTER	PR	DIFF	WASMTIME OVERHEAD
execute/ bare_call_0	1.01ms	1.01ms	🟢 -0.64%	1.02ms	934.94µs	🟢 -8.19%	🟢 -7%
execute/ bare_call_0/typed	526.24µs	519.89µs	🟢 -1.26%	453.96µs	453.80µs	⚪ -0.03%	🟢 -13%
execute/ bare_call_1	1.06ms	1.05ms	🔴 -0.79%	1.20ms	1.19ms	🔴 -0.88%	🟢 13%
execute/ bare_call_16	2.23ms	2.22ms	🔴 0.43%	4.94ms	4.74ms	🔴 -4.12%	🔴 113%
execute/ bare_call_16/typed	1.27ms	1.53ms	🔴 20.41%	2.40ms	2.47ms	🔴 3.00%	🟡 62%
execute/ bare_call_1/typed	608.31µs	602.84µs	⚪ -0.90%	762.88µs	770.28µs	⚪ 1.08%	🟢 28%
execute/ bare_call_4	1.18ms	1.19ms	🔴 1.13%	1.96ms	1.94ms	⚪ -1.08%	🟡 62%
execute/ bare_call_4/typed	621.18µs	638.39µs	🔴 2.78%	870.32µs	875.47µs	⚪ 0.31%	🟢 37%
execute/ br_table	623.22µs	626.93µs	⚪ 0.43%	958.42µs	944.79µs	🟢 -1.63%	🟡 51%
execute/ count_until	651.87µs	651.19µs	⚪ -0.23%	2.06ms	2.06ms	⚪ -0.12%	🔴 216%
execute/ factorial_iterative	312.27µs	307.44µs	🟢 -1.79%	867.95µs	863.72µs	⚪ -0.54%	🔴 181%
execute/ factorial_recursive	604.12µs	640.36µs	🔴 5.99%	1.32ms	1.31ms	⚪ -0.50%	🔴 105%
execute/ fib_iterative	1.55ms	1.43ms	🟢 -7.38%	4.69ms	4.65ms	⚪ -0.74%	🔴 225%
execute/ fib_recursive	5.83ms	5.79ms	⚪ -0.64%	12.13ms	11.88ms	🟢 -1.92%	🔴 105%
execute/ global_bump	952.27µs	948.93µs	⚪ -0.19%	3.11ms	3.12ms	⚪ 0.30%	🔴 229%
execute/ global_const	799.16µs	717.58µs	🟢 -10.31%	2.37ms	2.42ms	⚪ 2.75%	🔴 237%
execute/ host_calls	29.09µs	28.63µs	🟢 -1.74%	45.20µs	42.39µs	🟢 -6.36%	🟢 48%
execute/ memory_fill	1.30ms	1.28ms	🟢 -1.71%	4.15ms	4.11ms	⚪ -1.01%	🔴 221%
execute/ memory_sum	1.33ms	1.60ms	🔴 16.85%	4.15ms	4.13ms	⚪ -0.52%	🔴 158%
execute/ memory_vec_add	2.74ms	2.60ms	🟢 -5.08%	8.58ms	8.48ms	⚪ -1.06%	🔴 227%
execute/ recursive_is_even	1.12ms	1.12ms	⚪ 0.52%	2.17ms	2.14ms	🟢 -1.25%	🟡 90%
execute/ recursive_ok	142.90µs	145.80µs	🔴 1.99%	299.58µs	304.36µs	🔴 1.74%	🔴 109%
execute/ recursive_scan	178.06µs	179.06µs	⚪ 0.63%	385.43µs	390.21µs	⚪ 1.22%	🔴 118%
execute/ recursive_trap	13.99µs	14.34µs	🔴 2.48%	29.98µs	30.67µs	🔴 2.31%	🔴 114%
execute/ regex_redux	543.18µs	542.09µs	⚪ -0.22%	1.55ms	1.52ms	🟢 -1.38%	🔴 181%
execute/ rev_complement	517.99µs	506.68µs	🟢 -2.34%	1.52ms	1.52ms	⚪ -0.04%	🔴 200%
execute/ tiny_keccak	370.04µs	373.52µs	⚪ 0.67%	1.25ms	1.26ms	⚪ 0.50%	🔴 236%
execute/ trunc_f2i	922.62µs	909.70µs	🟢 -1.32%	2.49ms	2.49ms	⚪ 0.18%	🔴 174%
instantiate/ wasm_kernel	60.58µs	60.63µs	⚪ -2.23%	94.03µs	98.06µs	🔴 3.82%	🟡 62%
translate/ erc1155	204.50µs	208.47µs	🔴 2.11%	402.02µs	412.12µs	🔴 2.36%	🟡 98%
translate/ erc20	100.74µs	100.28µs	⚪ -0.52%	196.64µs	203.36µs	🔴 3.18%	🔴 103%
translate/ erc721	143.94µs	146.10µs	🔴 1.66%	287.02µs	293.30µs	🔴 2.03%	🔴 101%
translate/ spidermonkey	0.00ns	0.00ns	⚪ 0.19%	0.00ns	0.00ns	🔴 1.72%	🟢 0%
translate/ wasm_kernel	3.72ms	3.75ms	⚪ 0.43%	7.60ms	7.74ms	🔴 1.97%	🔴 106%

Link to pipeline