update signatures of method contains and explain handling of Cool params

If $needle and/or $pos is of type Cool, this is no longer directly handled by
a multi of Str.contains, but by a multi of Cool.contains.
Hence, remove such signatures from here and instead add an explanation
and a link to Cool.contains .
Also, order the signatures in a way that's better to digest.

Author: schultzdavid

doc/Type/Str.rakudoc

@@ -45,13 +45,15 @@ Examples:
 
 =head2 method contains
 
-    multi method contains(Str:D: Cool:D $needle, :i(:$ignorecase), :m(:$ignoremark) --> Bool:D)
-    multi method contains(Str:D: Str:D $needle, :i(:$ignorecase), :m(:$ignoremark) --> Bool:D)
-    multi method contains(Str:D: Regex:D $needle --> Bool:D)
-    multi method contains(Str:D: Cool:D $needle, Int(Cool:D) $pos, :i(:$ignorecase), :m(:$ignoremark) --> Bool:D)
-    multi method contains(Str:D: Str:D $needle, Int:D $pos, :i(:$ignorecase), :m(:$ignoremark) --> Bool:D)
-    multi method contains(Str:D: Regex:D $needle, Int:D $pos --> Bool:D)
-    multi method contains(Str:D: Regex:D $needle, Cool:D $pos --> Bool:D)
+    multi method contains(Str:D $:: Str:D $needle --> Bool)
+    multi method contains(Str:D $:: Str:D $needle, Int:D $pos --> Bool)
+    multi method contains(Str:D $:: Str:D $needle, :m(:$ignoremark)! --> Bool)
+    multi method contains(Str:D $:: Str:D $needle, :i(:$ignorecase)!, :m(:$ignoremark) --> Bool)
+    multi method contains(Str:D $:: Str:D $needle, Int:D $pos, :m(:$ignoremark)! --> Bool)
+    multi method contains(Str:D $:: Str:D $needle, Int:D $pos, :i(:$ignorecase)!, :m(:$ignoremark) --> Bool)
+    multi method contains(Str:D $:: Regex:D $needle --> Bool)
+    multi method contains(Str:D $:: Regex:D $needle, Int:D $pos --> Bool)
+
 
 Given a C<Str> invocant (known as the I<haystack>) and a first argument
 (known as the C<$needle>), it searches for the C<$needle> in the I<haystack>
@@ -71,6 +73,13 @@ invocant right from the start of the invocant string and returns C<True>.
 In the third case, the C<'Hello'> string is not found since we have
 started looking from the second position (index 1) in C<'Hello, World'>.
 
+C<$needle> can also be of type C<Cool>, which will be coerced to C<Str>.
+Similarly, C<$pos> can be of type C<Cool>, which will be coerced to C<Int>.
+(Technically, these cases will take a detour over L<C<Cool.contains>|/type/Cool#method_contains>,
+which does the coercions and then calls C<Str.contains>.)
+
+    say "Hello, 12345".contains(5, "10.0");     # OUTPUT: «True␤»
+
 Since Rakudo release 2020.02, the C<$needle> can also be
 a L<C<Regex>|/type/Regex> in which case the C<contains> method
 quickly returns whether the regex matches the string at least