Add support for SubValues and UpValues definitions

[batracos]

These syntaxes are not supported yet

  f[x_][y_] := x*y
(*^ entity.name.function*)

  f /: g[f[a_]] := a
(*^ entity.name.function*)
(*     ^variable.function.wolfram *)

[chere005]

How is f[x_][y_] := x*y not supported yet?