wasm: keep load values on the stack

We internally use a lot of `load`'s that used to put
the result in a newly created local. For instance, when is considered
byRef or when we need a specific field/element/bytes from a larger type.
However, sometimes we want to directly use this value and then forget about
it, which means storing it in a local first is wasted instructions as well
as wasted locals that shouldn't be generated in the first place.
With this change it's explicit and requires the usage of `toLocal`.

Author: Luukdegram