Add missing pg_description strings for pg_type entries.

I noticed that all non-composite, non-array entries in pg_type.dat
had descr strings, except for "json" and the pseudo-types.  The
lack for json seems certainly an oversight, and there's surely
little reason to not have entries for the pseudo-types either.
So add some.

"make reformat-dat-files" turned up some formatting issues in
pg_amop.dat, too, so fix those in passing.

No catversion bump since the backend doesn't care too much what is
in pg_description.

src/tools/pgindent/README

@@ -48,6 +48,12 @@ DOING THE INDENT RUN:
    If you want to use some perltidy version that's not in your PATH,
    first set the PERLTIDY environment variable to point to it.
 
+5) Reformat the bootstrap catalog data files:
+
+	cd src/include/catalog
+	make reformat-dat-files
+	cd ../../..
+
 VALIDATION:
 
 1) Check for any newly-created files using "git status"; there shouldn't