Make Rat.FatRat about 5x as fast

Since the Rat's attributes are already normalized, there is no
reason to go through the whole normalization process again.

This also affects FatRat literals in the form 0.1234.FatRat, as
these are currently codegenned as Rat WVal's with the .FatRat
method called on them at runtime.

src/core.c/Rat.pm6

@@ -4,7 +4,12 @@ my class Rat is Cool does Rational[Int, Int] {
         self
     }
     method FatRat(Rat:D: Real $? --> FatRat:D) {
-        FatRat.new($!numerator, $!denominator)
+        nqp::p6bindattrinvres(
+          nqp::p6bindattrinvres(
+            nqp::create(FatRat),FatRat,'$!numerator',$!numerator
+          ),
+          FatRat,'$!denominator',$!denominator
+        )
     }
     multi method raku(Rat:D: --> Str:D) {
         if $!denominator == 1 {