Supply an Any.match method candidate for Any:D

This addresses the use of non-`Str` candidates arriving
in `where` constraints that attempt to match against
a regex. (R#5464 / #5464).

```
subset S where { m/"aaa"/ }
class C { method Str { "aaa" } }
my S $s = C.new
```

The same error occurs with where clauses on signature
parameters.

This can still fail if you are trying to match against
an instance of an Any class that does not supply a Str
method. However, this seems like a reasonable site for
such a concern to be raised.

The Any:U candidate (formerly the only candidate) is
useful for issuing the standard warning for trying to
stringify a type object. It is worth noting that
removing it causes issues with running a test case
in `t/spec/S05-substitution/subst.t`:

```
$_ = Any;
s[ea] = "rea";
is $_, "", 'can use s[]="" when $_ is not set';
```

This test case is marked as TODO.

src/core.c/Any.rakumod

@@ -145,7 +145,9 @@ my class Any { # declared in BOOTSTRAP
 
     multi method iterator(Any:) { self.list.iterator }
 
-    method match(Any:U: |) { self.Str; nqp::getlexcaller('$/') = Nil }
+    proto method match(|)         {*}
+    multi method match(Any:U: |)  { self.Str; nqp::getlexcaller('$/') = Nil }
+    multi method match(Any:D: |c) { self.Str.match(|c) }
 
     proto method classify(|) is nodal {*}
     multi method classify() {