pg_stat_statements: Add tests with extended query protocol

There are currently no tests in the tree checking that queries using the
extended query protocol are able to map with their query ID.

This can be achieved for some paths of the extended query protocol with
the psql meta-commands \bind or \bind_named, so let's add some tests
based on both.

I have found that to be a useful addition while working on a different
issue.

Discussion: https://postgr.es/m/ZuEt6MOEBSlifBfn@paquier.xyz

contrib/pg_stat_statements/expected/extended.out

@@ -0,0 +1,62 @@
+-- Tests with extended query protocol
+SET pg_stat_statements.track_utility = FALSE;
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT $1 \parse stmt1
+SELECT $1, $2 \parse stmt2
+SELECT $1, $2, $3 \parse stmt3
+SELECT $1 \bind 'unnamed_val1' \g
+   ?column?   
+--------------
+ unnamed_val1
+(1 row)
+
+\bind_named stmt1 'stmt1_val1' \g
+  ?column?  
+------------
+ stmt1_val1
+(1 row)
+
+\bind_named stmt2 'stmt2_val1' 'stmt2_val2' \g
+  ?column?  |  ?column?  
+------------+------------
+ stmt2_val1 | stmt2_val2
+(1 row)
+
+\bind_named stmt3 'stmt3_val1' 'stmt3_val2' 'stmt3_val3' \g
+  ?column?  |  ?column?  |  ?column?  
+------------+------------+------------
+ stmt3_val1 | stmt3_val2 | stmt3_val3
+(1 row)
+
+\bind_named stmt3 'stmt3_val4' 'stmt3_val5' 'stmt3_val6' \g
+  ?column?  |  ?column?  |  ?column?  
+------------+------------+------------
+ stmt3_val4 | stmt3_val5 | stmt3_val6
+(1 row)
+
+\bind_named stmt2 'stmt2_val3' 'stmt2_val4' \g
+  ?column?  |  ?column?  
+------------+------------
+ stmt2_val3 | stmt2_val4
+(1 row)
+
+\bind_named stmt1 'stmt1_val1' \g
+  ?column?  
+------------
+ stmt1_val1
+(1 row)
+
+SELECT calls, rows, query FROM pg_stat_statements ORDER BY query COLLATE "C";
+ calls | rows |                       query                        
+-------+------+----------------------------------------------------
+     3 |    3 | SELECT $1
+     2 |    2 | SELECT $1, $2
+     2 |    2 | SELECT $1, $2, $3
+     1 |    1 | SELECT pg_stat_statements_reset() IS NOT NULL AS t
+(4 rows)
+