Specialise tc_eq_type to call patterns
As of today (0dba7841) GHC.Tc.Utils.TcType.tc_eq_type
takes two "mode" flags determining whether type synonyms should be expanded and whether invisible arguments should be considered. These two flags result in a fair amount of unneccesary allocation, especially given that these two flags are essentially always statically known at the call-site (which are all defined in the same moduel).
To avoid this I suggest we inline tc_eq_type
into its four call sites, allowing each to specialise to its mode flags.