feat(Linker): remove externals from Linker and make instantiate to use &self

[yjhmelody]

Just a previous PR, but I mainly want to generalize instantiate method

[yjhmelody]

🤔 Maybe I should not alter this method and just add a new one?

[paritytech-cicd-pr]

BENCHMARKS

	NATIVE			WASMTIME
BENCHMARK	MASTER	PR	DIFF	MASTER	PR	DIFF	WASMTIME OVERHEAD
execute/ count_until	947.12µs	918.74µs	🟢 -3.17%	2.38ms	2.38ms	⚪ 0.00%	🔴 159%
execute/ factorial_iterative	401.70ns	398.65ns	⚪ -0.80%	997.16ns	998.89ns	⚪ 0.26%	🔴 151%
execute/ factorial_recursive	763.97ns	783.94ns	🔴 2.67%	1.55µs	1.57µs	⚪ 0.70%	🟡 100%
execute/ fib_iterative	1.80ms	1.87ms	🔴 3.74%	5.11ms	5.11ms	⚪ -0.04%	🔴 174%
execute/ fib_recursive	7.01ms	7.16ms	🔴 2.22%	14.03ms	14.29ms	🔴 1.93%	🟡 99%
execute/ global_bump	1.48ms	1.36ms	🟢 -7.84%	3.64ms	4.63ms	🔴 27.16%	🔴 240%
execute/ host_calls	32.00µs	32.32µs	⚪ 0.19%	45.20µs	45.11µs	⚪ -0.21%	🟢 40%
execute/ memory_fill	1.67ms	1.70ms	🔴 1.64%	4.33ms	4.33ms	⚪ -0.18%	🔴 155%
execute/ memory_sum	1.57ms	1.59ms	🔴 1.28%	4.36ms	4.36ms	⚪ -0.03%	🔴 174%
execute/ memory_vec_add	3.25ms	3.16ms	🟢 -2.72%	8.94ms	8.94ms	⚪ -0.02%	🔴 183%
execute/ recursive_is_even	1.35ms	1.35ms	⚪ -0.11%	2.55ms	2.57ms	⚪ 0.68%	🟡 90%
execute/ recursive_ok	179.57µs	181.76µs	🔴 1.29%	349.32µs	356.84µs	🔴 2.19%	🟡 96%
execute/ recursive_scan	219.62µs	216.80µs	⚪ -1.47%	485.37µs	460.62µs	🟢 -5.20%	🔴 112%
execute/ recursive_trap	17.73µs	17.21µs	🟢 -2.97%	36.89µs	35.75µs	🟢 -3.28%	🔴 108%
execute/ regex_redux	676.86µs	720.77µs	🔴 6.83%	1.60ms	1.62ms	🔴 1.60%	🔴 125%
execute/ rev_complement	625.28µs	618.27µs	🟢 -1.24%	1.55ms	1.56ms	⚪ 0.74%	🔴 153%
execute/ tiny_keccak	485.53µs	514.71µs	🔴 6.75%	1.48ms	1.42ms	🟢 -4.28%	🔴 175%
execute/ trunc_f2i	1.01ms	1.02ms	⚪ 0.69%	2.74ms	2.72ms	⚪ -0.51%	🔴 166%
instantiate/ wasm_kernel	67.73µs	67.77µs	⚪ 0.79%	126.62µs	94.25µs	🟢 -25.43%	🟢 39%
translate/ wasm_kernel	4.83ms	4.83ms	⚪ -0.12%	9.58ms	9.27ms	🟢 -3.30%	🟡 92%

Link to pipeline

[Robbepop]

Hmmm this is already the 2nd time you requested this PR.
However, I took another look and the Wasmtime API also takes a &self reference for the Linker::instantiate method. So this is indeed bad since we ideally want to mirror the Wasmtime API as closely as possible.
Since your changes do not display significant performance differences I am inclined to actually merging it. However, it is not ideal since we are (again) very dependent on Rust and LLVM optimizing the allocations away. If those optimizations no longer apply we will see significant regressions.

[yjhmelody]

@Robbepop you could keep the inner buf, but add a &mut self version.

[Robbepop]

@Robbepop you could keep the inner buf, but add a &mut self version.

As I said we want to closely mirror the Wasmtime API and since the Wasmtime API does not have 2 APIs for that functionality we won't introduce them either.