Checkdoc fixes in `textmodes/*.el`

Checkdoc fixes in `textmodes/*.el`

* lisp/textmodes/ispell.el (ispell-command-loop):
* lisp/textmodes/mhtml-mode.el (mhtml--construct-submode):
* lisp/textmodes/page-ext.el (pages-set-delimiter):
* lisp/textmodes/refbib.el (r2b-get-field, r2b-put-field):
* lisp/textmodes/refer.el (refer-cache-bib-files):
* lisp/textmodes/reftex-index.el (reftex-index-phrase-selection-or-word):
(reftex-index-phrases-mode):
* lisp/textmodes/table.el (table-insert, table--fill-region-strictly):
Checkdoc fixes.

(cherry picked from commit 336aa6ab17a25351d54bb66fb66939ca27a6e94a)