Attempt to add 'case statements' to indexing

This is just for a search convenience if someone
coming from a C-style language background searches for 'case' or
'case statements' instead of 'switch'.

Author: Michael-S

doc/Language/control.pod6

@@ -776,7 +776,7 @@ L<supply|/language/concurrency#index-entry-supply_(on-demand)>:
     # received Rat (0.5)
 
 =head1 X<given|control flow, given>
-X<|switch (given)>
+X<|switch (given);case statements (given)>
 
 The C<given> statement is Raku's topicalizing keyword in a similar way that
 C<switch> topicalizes in languages such as C. In other words, C<given>