SILGen: Carry WMO of type lowering context to closure captures.
TypeConverter doesn't know by itself what SILModule it's currently lowering on
behalf of, so the existing code forming the TypeExpansionContext for opaque types
incorrectly set the isWholeModule flag to always false. This created a miscompile
when a public API contained a closure that captured a value involving private types
from another file in the same module because of mismatched type expansion contexts
inside and outside the closure. Fixes rdar://93821679
