Use VisitOperator trait in new FuncTranslator

[Robbepop]

This PR carves out a FuncTranslator type from the big FuncBuilder type.
The FuncBuilder type now owns a FuncTranslator as one of its fields.
All translation logic now lives inside the FuncTranslator type.
The FuncTranslator properly implements the VisitOperator trait to translate functions.
The FuncBuilder has the job to validate any Wasm bytecode before translating it via the VisitOperator trait.

This PR goes one step further into a direction that will allow us to have a well defined interface for wasmi multi Engine backend support.

[paritytech-cicd-pr]

BENCHMARKS

	NATIVE			WASMTIME
BENCHMARK	MASTER	PR	DIFF	MASTER	PR	DIFF	WASMTIME OVERHEAD
execute/ bare_call_0	1.46ms	1.40ms	🟢 -4.43%	1.16ms	1.16ms	⚪ 0.76%	🟢 -17%
execute/ bare_call_0/typed	1.09ms	1.02ms	🟢 -6.05%	784.02µs	779.78µs	⚪ -0.30%	🟢 -24%
execute/ bare_call_1	1.51ms	1.44ms	🔴 -4.82%	1.40ms	1.43ms	🔴 2.46%	🟢 -0%
execute/ bare_call_16	2.37ms	2.50ms	🔴 4.68%	4.45ms	4.46ms	🔴 0.40%	🟡 78%
execute/ bare_call_16/typed	1.83ms	1.82ms	⚪ -1.08%	2.80ms	2.84ms	🔴 1.31%	🟡 56%
execute/ bare_call_1/typed	1.21ms	1.14ms	🟢 -5.80%	1.18ms	1.22ms	🔴 2.61%	🟢 7%
execute/ bare_call_4	1.61ms	1.59ms	🟢 -1.11%	2.03ms	2.02ms	⚪ -0.24%	🟢 27%
execute/ bare_call_4/typed	1.19ms	1.14ms	🟢 -3.17%	1.31ms	1.30ms	⚪ -0.67%	🟢 14%
execute/ br_table	1.17ms	1.19ms	🔴 1.12%	1.37ms	1.36ms	⚪ -0.46%	🟢 15%
execute/ count_until	682.99µs	682.83µs	⚪ 0.00%	2.12ms	2.15ms	⚪ 1.47%	🔴 214%
execute/ factorial_iterative	328.30µs	326.13µs	⚪ -0.67%	946.57µs	950.10µs	⚪ 0.25%	🔴 191%
execute/ factorial_recursive	658.91µs	654.22µs	⚪ -0.67%	1.34ms	1.35ms	⚪ 0.10%	🔴 106%
execute/ fib_iterative	1.40ms	1.40ms	⚪ 0.15%	5.15ms	5.18ms	⚪ 0.44%	🔴 270%
execute/ fib_recursive	6.06ms	5.94ms	🟢 -2.26%	11.99ms	11.75ms	🟢 -2.02%	🟡 98%
execute/ global_bump	983.93µs	983.63µs	⚪ 0.08%	2.48ms	2.45ms	🟢 -1.31%	🔴 149%
execute/ global_const	741.96µs	742.27µs	⚪ 0.03%	2.55ms	2.55ms	⚪ 0.05%	🔴 244%
execute/ host_calls	25.96µs	26.00µs	⚪ 0.12%	39.44µs	39.05µs	⚪ -1.14%	🟢 50%
execute/ memory_fill	1.25ms	1.25ms	⚪ -0.25%	4.15ms	4.16ms	⚪ 0.06%	🔴 232%
execute/ memory_sum	1.19ms	1.19ms	⚪ 0.06%	4.15ms	4.16ms	⚪ 0.46%	🔴 248%
execute/ memory_vec_add	2.60ms	2.60ms	⚪ -0.03%	7.59ms	7.60ms	⚪ 0.20%	🔴 192%
execute/ recursive_is_even	1.12ms	1.17ms	🔴 4.75%	2.33ms	2.29ms	🟢 -2.15%	🟡 95%
execute/ recursive_ok	157.75µs	158.89µs	⚪ 0.70%	340.51µs	315.58µs	🟢 -7.20%	🟡 99%
execute/ recursive_scan	186.34µs	182.61µs	⚪ -1.51%	404.94µs	380.32µs	🟢 -6.02%	🔴 108%
execute/ recursive_trap	15.88µs	16.45µs	🔴 3.49%	29.69µs	31.65µs	🔴 6.45%	🟡 92%
execute/ regex_redux	530.62µs	525.83µs	⚪ -0.85%	1.42ms	1.38ms	🟢 -2.32%	🔴 163%
execute/ rev_complement	487.72µs	493.98µs	🔴 1.49%	1.43ms	1.42ms	⚪ -0.86%	🔴 187%
execute/ tiny_keccak	350.99µs	335.29µs	🟢 -4.54%	1.16ms	1.16ms	⚪ 0.95%	🔴 247%
execute/ trunc_f2i	735.08µs	734.24µs	⚪ -0.04%	2.13ms	2.13ms	⚪ -0.09%	🔴 190%
instantiate/ wasm_kernel	64.79µs	64.41µs	⚪ -3.54%	72.51µs	71.74µs	⚪ 0.13%	🟢 11%
translate/ erc1155	204.32µs	209.37µs	🔴 2.31%	388.89µs	386.04µs	⚪ -0.73%	🟡 84%
translate/ erc20	100.10µs	102.75µs	🔴 2.22%	191.20µs	190.99µs	⚪ 0.08%	🟡 86%
translate/ erc721	143.62µs	146.29µs	🔴 1.87%	277.80µs	278.72µs	⚪ 0.30%	🟡 91%
translate/ spidermonkey	0.00ns	0.00ns	🔴 2.37%	0.00ns	0.00ns	⚪ 0.20%	🟢 0%
translate/ wasm_kernel	3.71ms	3.78ms	🔴 1.78%	7.27ms	7.24ms	⚪ -0.43%	🟡 92%

Link to pipeline