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/sql/test_parser.sql

@@ -0,0 +1,18 @@
+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/');
+
+SELECT to_tsvector('testcfg','That''s my first own parser');
+
+SELECT to_tsquery('testcfg', 'star');
+
+SELECT ts_headline('testcfg','Supernovae stars are the brightest phenomena in galaxies',
+       to_tsquery('testcfg', 'stars'));