[wasm] Experiment with emscripten settings to shrink binary size

[CoffeeFlux]

The emscripten settings file defines a lot of different settings we could possibly set to get size wins without too much effort, but it's hard to ballpark how much of a difference these will make.

Some options that appear initially promising:

• dlmalloc - we could switch to a more compact implementation, or just remove this entirely from mono-codeman.c
• EVAL_CTORS - this tries to evaluate global ctors at compile-time, and might potentially give us size wins on the ICU builds?
• INCOMING_MODULE_JS_API - we probably don't need most of these?
• WebGL - there are a lot of random WebGL settings that might be keeping things around?
• ASSERTIONS - this adds runtime assertions that we may not need but bloat the code size

[CoffeeFlux]

Some experiments done, but the results are not very promising.

[lewing]

closing this