This switches our wasm build to use "shared" memory. Shared memory can
be shared across multiple web workers, which is something we'll want to
support for our multi-threaded behaviors later.
Shared memory has a number of different restrictions so this updates
zig-js to support it as well as updates some of our functions that need
to be aware of it.
We don't need the Atlas API for wasm at all, but its a good way to test
things work incrementally and its a pretty cool thing to have as a wasm
library really.
