Make sure that .of returns a type

Specifying a type object in a return constraint merely sets up a type
*check*, it does *not* actually return that type.  Fixes issue spotted
by b2gills++

src/core.c/Array.pm6

@@ -1277,7 +1277,7 @@ my class Array { # declared in BOOTSTRAP
     }
 
     proto method of() {*}
-    multi method of(Array:U: --> Mu) { }
+    multi method of(Array:U:) { Mu }
     multi method of(Array:D:) {
         nqp::isnull($!descriptor) ?? Mu !! $!descriptor.of
     }

src/core.c/Baggy.pm6

@@ -12,7 +12,7 @@ my role Baggy does QuantHash {
 # Immutables aspects of Bag/Mix, need to live to Bag/Mix respectively.
 
 #--- interface methods
-    method of(--> UInt) { }
+    method of() { UInt }
 
     multi method ACCEPTS(Baggy:U: \other --> Bool:D) {
         other.^does(self)

src/core.c/Block.pm6

@@ -5,7 +5,7 @@ my class Block { # declared in BOOTSTRAP
     #     has Mu $!why;
 
     proto method of() {*}
-    multi method of(Block:U: --> Mu) { }
+    multi method of(Block:U:) { Mu }
     multi method of(Block:D:) { nqp::getattr(self,Code,'$!signature').returns }
 
     method returns(Block:D:) { nqp::getattr(self,Code,'$!signature').returns }

src/core.c/Hash.pm6

@@ -210,7 +210,7 @@ my class Hash { # declared in BOOTSTRAP
     method keyof() { Str(Any) }  # overridden by Hash::Object
 
     proto method of() {*}
-    multi method of(Hash:U: --> Mu) { }
+    multi method of(Hash:U:) { Mu }
     multi method of(Hash:D:) { $!descriptor.of }
 
     method name(Hash:D:)    { $!descriptor.name }

src/core.c/IO/Path/Parts.pm6

@@ -27,7 +27,7 @@ class IO::Path::Parts
 # original List of Pairs / Map implementation.  As soon as this is no longer
 # needed, this can go.
 
-    method of(--> Str) { }
+    method of() { Str }
 
     method iterator() { (:$!volume, :$!dirname, :$!basename).iterator }
 

src/core.c/Mixy.pm6

@@ -1,6 +1,6 @@
 my role Mixy does Baggy  {
 
-    method of(--> Real) { }
+    method of() { Real }
 
     multi method hash(Mixy:D: --> Hash:D) { self!HASHIFY(Real) }
     multi method Hash(Mixy:D: --> Hash:D) { self!HASHIFY(Any) }

src/core.c/Scalar.pm6

@@ -20,7 +20,7 @@ my class Scalar { # declared in BOOTSTRAP
     }
 
     proto method of() {*}
-    multi method of(Scalar:U: --> Mu) { }
+    multi method of(Scalar:U:) { Mu }
     multi method of(Scalar:D:) {
         nqp::isnull($!descriptor) ?? Mu !! $!descriptor.of
     }

src/core.c/Setty.pm6

@@ -1,7 +1,7 @@
 my role Setty does QuantHash {
     has Rakudo::Internals::IterationSet $!elems; # key.WHICH => key
 
-    method of(--> Bool) { }
+    method of() { Bool }
 
     # private method to create Set from iterator, check for laziness
     method !create-from-iterator(\type, \iterator --> Setty:D) {