wasm: Refactor stack to account for alignment
wasm: Refactor stack to account for alignment

We now calculate the total stack size required for the current frame.
The default alignment of the stack is 16 bytes, and will be overwritten when the alignment
of a given type is larger than that.

After we have generated all instructions for the body, we calculate the total stack size
by forward aligning the stack size while accounting for the max alignment.
We then insert a prologue into the body, where we substract this size from the stack pointer
and save it inside a bottom stackframe local. We use this local then, to calculate
the stack pointer locals of all variables we allocate into the stack.

In a future iteration we can improve this further by storing the offsets as a new `stack_offset` `WValue`.
This has the benefit of not having to spend runtime cost of storing those offsets, but instead we append
those offsets whenever we need the value that lives in the stack.

andrewrk/zig,andrewrk/zig