Analyze component instantiation to find constant values of immutable global imports

[fitzgen]

After #12234, we will emit inline constants for immutable+defined globals, but we cannot do the same for immutable+imported without

1. an analysis (similar to our known imported function analysis) to find the globals that the satisfy that import
2. checking that the import is always satisfied with a global of the same value
3. checking that the module is not exported (which would allow instantiating it in host code with a global of a different value)

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One possible future extension (not for this PR of course) would be to do something similar to the inliner to record that, even for imported globals, if the definition is in-wasm itself then we can also use the constant value. (e.g. dynamic-linking-using modules in components have this use case a lot)

Originally posted by @alexcrichton in #12234 (comment)