Extend instantiate() with a memory limit

[axic]

This would replace the hard MemoryPagesLimit in limits.h. If no limit is set by the user, it defaults to MemoryPagesLimit (256Mb). If it is set higher than 2^32-1 return an error (or just make the limit uint32).

Also set this limit to 4Gb in spectests in order to pass them.

[gumb0]

1. 4Gb limit is already enforced by validation, do we want a new error raised when incorrect limit passed to instantiate?

2. memory.grow currently also aborts when exceeding MemoryPagesLimit. We would need to save the hard limit to Instance to use it in execute, too.

[axic]

All we want is a new configurable limit (part of the Instance). We can default to our 256Mb limit if it is not set my the user.