Change WASM direct heap access to use helper functions (#61355)

Change WASM direct heap access to use helper functions (#61355)

Direct heap writes via Module.HEAPxx[y] = func(...) are incorrect because the left-hand side (according to spec) is evaluated before the right, so if evaluating func(...) causes the heap to grow, the assignment target becomes a detached buffer and the write goes nowhere, breaking your application. This PR introduces a new set of helper functions for memory reads and writes.