prefer-inline pragmas are not sufficient to do the inlining we want

[osa1]

import 'dart:typed_data';

@pragma("wasm:prefer-inline")
int sum(List<int> list) {
  int ret = 0;
  for (int i = 0; i < list.length; i += 1) {
    ret += list[i];
  }
  return ret;
}

void main() {
  Int64List intList = Int64List.fromList([1, 2, 3, 4]);
  sum(intList);
  sum([1, 2, 3, 4]);
}

Ideally we want all direct calls to Int64List.[] to be inlined:

sdk/sdk/lib/_internal/wasm/lib/typed_data.dart

Lines 3054 to 3059 in e87c93b

	@override
	@pragma("wasm:prefer-inline")
	int operator [](int index) {
	indexCheck(index, length);
	return _data.read(_offsetInElements + index);
	}

But when a call becomes direct after wasm-opt, because we can't control wasm-opt's inliner with a similar pragma, it's not inlined. Relevant parts of the output of the code above:

(func $main (;297;)
  ...
  loop $label1
    local.get $var7
    call $_WasmI64ArrayBase.length initializer
    local.get $var2
    i64.gt_s
    if
      local.get $var4
      local.get $var7
      local.get $var2
      call $I64List.[]
      ref.cast $BoxedInt
      struct.get $BoxedInt $field1
      i64.add
      local.set $var4
      local.get $var2
      i64.const 1
      i64.add
      local.set $var2
      br $label1
    end
  end $label1
  ...
)

Becuase [] is not inlined, each access to the array boxes the integer in the array before returning.