Add ImportResolver interface and use it for global imports

[stevenfontanella]

Add an ImportResolver interface with some implementations to handle the spec interpreter and ctor-eval

• Removes coupling of imported names from the module they come from. This will allows us to provide special imports like the spec test module better which have some 'magic' e.g. for printing functions which can't be implemented in Wasm (globals remain the same because they still come from a real module which is better).
• Removes pointer chasing logic when resolving imported globals in both cases.
• Also allows us to relax ctor-eval and allow programs that import globals to be optimized more (as long as they don't try to evaluate imports) Ctor-eval: Don't stop evaluating when an imported global isn't used #8168
• Fixes Segfault in ctor-eval when an imported global isn't used #8167
• Part of Refactorings to imports in Binaryen #8180

[tlively]

It would also be fine to over-reserve wasm->globals.size() slots.

[stevenfontanella]

Good point. I guess there's no harm in leaving it this way?