(pgsql) add test for $$ quoting existing behavior

- even if that existing behavior is questionable
- the ending span should really close before the $$, not after

Fixing this would involve delving into the sublanguage behavior and I'm
not sure we have time to tackle that right this moment.

test/markup/pgsql/dollar_strings.expect.txt

@@ -0,0 +1,9 @@
+<span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">OR REPLACE</span> <span class="hljs-keyword">FUNCTION</span> hello_world(param_your_name <span class="hljs-type">text</span>)
+<span class="hljs-keyword">RETURNS</span> <span class="hljs-type">text</span> <span class="hljs-keyword">AS</span>
+$$<span class="ruby">
+SELECT <span class="hljs-string">'Hello world. My name is '</span> <span class="hljs-params">||</span> param_your_name <span class="hljs-params">||</span> <span class="hljs-string">'.'</span>;
+$$</span>
+<span class="hljs-keyword">language</span> <span class="hljs-keyword">sql</span> <span class="hljs-keyword">STRICT</span>;
+
+<span class="hljs-keyword">SELECT</span> sql_expression($sql$<span class="ruby">SELECT hello_world($phrase$Regina<span class="hljs-string">'s elephant'</span>s dog$phrase$)
+    <span class="hljs-params">||</span> $phrase$ I made a cat<span class="hljs-string">'s meow today.$phrase$ $sql$</span></span>);

test/markup/pgsql/dollar_strings.txt

@@ -0,0 +1,9 @@
+CREATE OR REPLACE FUNCTION hello_world(param_your_name text)
+RETURNS text AS
+$$
+SELECT 'Hello world. My name is ' || param_your_name || '.';
+$$
+language sql STRICT;
+
+SELECT sql_expression($sql$SELECT hello_world($phrase$Regina's elephant's dog$phrase$)
+    || $phrase$ I made a cat's meow today.$phrase$ $sql$);