runtime(doc): fix help tags for removed/reused error codes

runtime(doc): fix help tags for removed/reused error codes

Problem:  Several error codes (E614, E1319, E1321, E1323, E1400, E1401,
          E1402, E1406) were removed from errors.h in v9.1.0600 but
          their *Ennn* tags remained in the help files, so :help Ennn
          jumps to obsolete locations.  E1395 was later reused with a
          new meaning ("Using a null class") in v9.1.1119, but its tag
          is still placed in the type-alias section.
Solution: Remove the stale *Ennn* tags from the help files.  Move
          *E1395* to the vim9.txt null-values section to match its
          current meaning.  Also fix the indentation of *E1411*.
          Regenerate runtime/doc/tags.

closes: #20279

Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>