Tuple and tuple struct fields always list completions for the first field

[jonas-schievink]

struct S(u8, String);

fn f(s: S) {
    s.1.$0
}

This incorrectly lists the methods of u8, not of String.

The same happens for the corresponding (u8, String) tuple type instead of S.

[Veykril]

Most likely happens due to us parsing the 1. in s.1. as float still cc #1109

FIELD_EXPR@2646..2650
  PATH_EXPR@2646..2647
    PATH@2646..2647
      PATH_SEGMENT@2646..2647
        NAME_REF@2646..2647
          IDENT@2646..2647 "x"
  DOT@2647..2648 "."
  FLOAT_NUMBER@2648..2650 "1."