Calling WASI `_start` causes some modules to exit

[ashtonmeuser]

There are two patterns of WASI Wasm modules: commands and reactors.

• Commands typically have a main function that is run after which the module exists (calls wasi_snapshot_preview1.proc_exit()). This main function is triggered by the modules exported _start() function.
• Reactors are longer-lived modules. If the module requires setup e.g. memory initialization, it should be done once after module instantiation and is triggered by the modules exported _initialize() function.

This is all well and good in theory but seems to be abused by many compilers targeting WebAssembly. It seems prudent to either:

1. Not call either _start() or _initialize() and leave this entirely up to the user of Godot Wasm.
2. Expose aa initialize setting on the Wasm class that allows a user to define the startup function to be immediately on module initialization.
3. Call _initialize(). This supports the reactor pattern as it will be interacted with by the user of Godot Wasm later via function(), global(), etc. To support the command pattern, the user has to simply call my_module.function("_start", []).

One thing is certain: Godot Wasm should not blindly call _start immediately on instantiation as it currently does.

[ashtonmeuser]

Solved in https://github.com/ashtonmeuser/godot-wasm/commit/58f8002f54a3f4dfab5066d74817a740fd43d7f9 using option 3 outline above.