[browser] fix 4GB JS interop

[pavelsavara]

This is use on your own risk

Even when we try to make this work, we do not think it's good idea to allocate more than 256MB in a web page.

• add new malloc which is wrapper over Module._malloc that returns uint32 rather than negative number above 2GB
• fix receiving pointers when calling to JS on via ICALL
• fix marshaling IntPtr as uint32 to JS, because typically it's used as offset to array
• add Module parameter to preRun and other emscripten events. So that it could be used to test memory.
• improved MemoryTest WBT to waste 2GB before starting the mono runtime.

[kg]

I like the incremental improvements you're making while doing this