Check for interrupts in pg_trgm word similarity

Calculating similarity between large strings can be timesconsuming
and overrun configured statement timeouts. Check for interrupts in
the main loop to ensure query cancellation can be performed.

Author: Robins Tharakan <tharakan@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAEP4nAxvmfc_XWTz73bqXRhgjONi=1HaX4_NhsopA3L6UvnN1g@mail.gmail.com

contrib/pg_trgm/trgm_op.c

@@ -7,6 +7,7 @@
 
 #include "catalog/pg_type.h"
 #include "lib/qunique.h"
+#include "miscadmin.h"
 #include "trgm.h"
 #include "tsearch/ts_locale.h"
 #include "utils/lsyscache.h"
@@ -492,8 +493,12 @@ iterate_word_similarity(int *trg2indexes,
 
 	for (i = 0; i < len2; i++)
 	{
+		int			trgindex;
+
+		CHECK_FOR_INTERRUPTS();
+
 		/* Get index of next trigram */
-		int			trgindex = trg2indexes[i];
+		trgindex = trg2indexes[i];
 
 		/* Update last position of this trigram */
 		if (lower >= 0 || found[trgindex])