Move test modules from contrib to src/test/modules

This is advance preparation for introducing even more test modules; the
easy solution is to add them to contrib, but that's bloated enough that
it seems a good time to think of something different.

Moved modules are dummy_seclabel, test_shm_mq, test_parser and
worker_spi.

(test_decoding was also a candidate, but there was too much opposition
to moving that one.  We can always reconsider later.)

src/test/modules/test_parser/expected/test_parser.out

@@ -0,0 +1,44 @@
+CREATE EXTENSION test_parser;
+-- make test configuration using parser
+CREATE TEXT SEARCH CONFIGURATION testcfg (PARSER = testparser);
+ALTER TEXT SEARCH CONFIGURATION testcfg ADD MAPPING FOR word WITH simple;
+-- ts_parse
+SELECT * FROM ts_parse('testparser', 'That''s simple parser can''t parse urls like http://some.url/here/');
+ tokid |         token         
+-------+-----------------------
+     3 | That's
+    12 |  
+     3 | simple
+    12 |  
+     3 | parser
+    12 |  
+     3 | can't
+    12 |  
+     3 | parse
+    12 |  
+     3 | urls
+    12 |  
+     3 | like
+    12 |  
+     3 | http://some.url/here/
+(15 rows)
+
+SELECT to_tsvector('testcfg','That''s my first own parser');
+                   to_tsvector                   
+-------------------------------------------------
+ 'first':3 'my':2 'own':4 'parser':5 'that''s':1
+(1 row)
+
+SELECT to_tsquery('testcfg', 'star');
+ to_tsquery 
+------------
+ 'star'
+(1 row)
+
+SELECT ts_headline('testcfg','Supernovae stars are the brightest phenomena in galaxies',
+       to_tsquery('testcfg', 'stars'));
+                           ts_headline                           
+-----------------------------------------------------------------
+ Supernovae <b>stars</b> are the brightest phenomena in galaxies
+(1 row)
+