Consolidate quietly into statement-prefix.pod6 from control.pod6. (#4151

)

* Consolidate quietly into statement-prefix.pod6 from control.pod6.

Planning to change the file name to prefixes.pod6 or modifiers.pod6
unless a better name emerges.

* Improve phrasing around "run-time" and eliminate a <ws>.

doc/Language/control.pod6

@@ -1159,22 +1159,6 @@ Note that this is B<not> a thread-safe construct when the same clone of the same
 block is run by multiple threads. Also remember that methods only have one
 clone per class, not per object.
 
-=head1 X<quietly|Control flow,quietly>
-
-A C<quietly> block will suppress all warnings generated in it.
-
-    quietly { warn 'kaput!' };
-    warn 'still kaput!';
-    # OUTPUT: «still kaput! [...]␤»
-
-Any warning generated from any routine called from within the block will also be
-suppressed:
-
-    sub told-you { warn 'hey...' };
-    quietly { told-you; warn 'kaput!' };
-    warn 'Only telling you now!'
-    # OUTPUT: «Only telling you now!␤ [...] ␤»
-
 
 =head1 LABELs
 

doc/Language/statement-prefixes.pod6

@@ -80,16 +80,18 @@ don't care.
 
 =head2 X<C<quietly>|Syntax,quietly (statement prefix)>
 
-As a statement prefix, C<quietly> suppresses all warnings produced by the
-statement it precedes.
+As a prefix, C<quietly> suppresses all run-time warnings produced by the
+block or statement it precedes.
 
 =for code
 sub marine() {};
 quietly say ~&marine; # OUTPUT: «marine␤»
+sub told-you { warn 'hey...' }; 
+quietly { told-you; warn 'kaput!' };
+warn 'Telling you now!';  # OUTPUT: «Telling you now!␤ [...] ␤»
 
 Calling L<C<.Str> on C<code> produces a warning|/type/Code#method_Str>.
-Preceding the statement with C<quietly > will just produce the output, the name
-of the routine.
+Preceding the code with C<quietly> will just produce the output without warning.
 
 =head2 X<C<try>|Syntax,try (statement prefix)>