Support comments in statements in JdbcTestUtils

Prior to this commit, executing an SQL script with JdbcTestUtils would
fail if a statement in the script contained a line comment within the
statement.

This commit ensures that standard SQL comments (i.e., any text beginning
with two hyphens and extending to the end of the line) are properly
omitted from the statement before executing it.

In addition, multiple adjacent whitespace characters within a statement
but outside a literal are now collapsed into a single space.

Issue: SPR-9982

spring-test/src/test/resources/org/springframework/test/jdbc/test-data-with-comments.sql

@@ -1,6 +1,16 @@
+-- The next comment line has no text after the '--' prefix.
+--
+-- The next comment line starts with a space.
+ -- x, y, z...
+
 insert into customer (id, name)
 values	(1, 'Rod; Johnson'), (2, 'Adrian Collier');
 -- This is also a comment.
 insert into orders(id, order_date, customer_id)
 values (1, '2008-01-02', 2);
-insert into orders(id, order_date, customer_id) values (1, '2008-01-02', 2);
+insert into orders(id, order_date, customer_id) values (1, '2008-01-02', 2);
+INSERT INTO persons( person_id--      
+                   , name)
+VALUES( 1      -- person_id
+      , 'Name' --name
+);--