Compute effects for indirect calls in GlobalEffects

[stevenfontanella]

When running in --closed-world, compute effects for indirect calls by unioning the effects of all potential functions of that type. In --closed-world, we assume that all references originate in our module, so the only possible functions that we don't know about are imports. Previously we gave up on effects analysis for indirect calls.

Yields a very small byte count reduction in calcworker (3799354 - 3799297 = 57 bytes). Also shows no significant difference in runtime: (0.1346069 -> 0.13375045 = <1% improvement, probably within noise). We expect more benefits after we're able to share indirect call effects with other passes, since currently they're only seen one layer up for callers of functions that indirectly call functions (see the newly-added tests for examples).

Followups:

• Share effect information per type with other passes besides just via Function::effects
• Exclude functions that don't have an address (i.e. functions that aren't the target of ref.func) from effect analysis
• Compute effects more precisely for exact + nullable/non-nullable references

Part of #8615.