[CIR][NFC] Eliminate ArgInfo structure (#140612)
A previous refactoring had reduced the ArgInfo structure to contain a
single member, the argument type. This change eliminates the ArgInfo
structure entirely, instead just storing the argument type directly in
places where ArgInfo had previously been used.
This also updates the place where the arg types were previously being
copied for a call to CIRGenFunctionInfo::Profile to instead use the
stored argument types buffer directly and adds assertions where the
calculated folding set ID is used to verify that any match was correct.
