Use a common set of string delimiters for all Eshell predicates/modifiers

Use a common set of string delimiters for all Eshell predicates/modifiers

* lisp/eshell/em-pred.el (eshell-pred-delimiter-pairs): New variable.
(eshell-get-comparison-modifier-argument)
(eshell-get-numeric-modifier-argument)
(eshell-get-delimited-modifier-argument): New functions...
(eshell-pred-user-or-group, eshell-pred-file-time)
(eshell-pred-file-links, eshell-pred-file-size)
(eshell-pred-substitute, eshell-join-memebers, eshell-split-members):
... and use them here.
(eshell-include-members): Pass 'mod-char' and use
'eshell-get-delimited-modifier-argument'.
(eshell-pred-file-type, eshell-pred-file-mode): Use 'when-let'.
(eshell-modifier-alist): Pass modifier char to
'eshell-include-members'.

* test/lisp/eshell/em-pred-tests.el
(em-pred-test/predicate-delimiters): New test.
(em-pred-test/predicate-uid, em-pred-test/predicate-gid,
em-pred-test/modifier-include, em-pred-test/modifier-exclude): Remove
cases covered by 'em-pred-test/predicate-delimiters'.
(em-pred-test/modifier-substitute): Add test cases for new delimiter
styles.

* doc/misc/eshell.texi (Argument Predication and Modification):
Explain how string parameters are delimited.
(Argument Modifiers): Document some special delimiter behavior with
the 's/PATTERN/REPLACE/' modifier (bug#55204).

* etc/NEWS: Announce this change, and move the
'eshell-eval-using-options' entry to the Eshell section.