Evaluate eql specializers

Evaluate eql specializers

* lisp/emacs-lisp/cl-generic.el (cl-generic-generalizers): Evaluate
forms that are eql specializers.  Provide backward compatibility
with a warning.

* test/lisp/emacs-lisp/cl-generic-tests.el: Add a test.
* lisp/emacs-lisp/bindat.el (bindat--type): Adhere to the new rule.
* lisp/emacs-lisp/edebug.el (edebug--match-&-spec-op): Adhere to the new rule.
* lisp/emacs-lisp/map.el (map-into): Adhere to the new rule.
* lisp/emacs-lisp/radix-tree.el (map-into): Adhere to the new rule.
* lisp/frame.el (cl-generic-define-context-rewriter): Adhere to the new rule.
* lisp/gnus/gnus-search.el
(gnus-search-transform-expression): Adhere to the new rule.
* lisp/image/image-converter.el
(image-converter--probe image-converter--convert): Adhere to the new rule.
* lisp/mail/smtpmail.el (smtpmail-try-auth-method): Adhere to the new rule.
* lisp/progmodes/elisp-mode.el
(xref-backend-definitions)
(xref-backend-apropos): Adhere to the new rule.
* lisp/progmodes/etags.el (xref-backend-identifier-at-point)
(xref-backend-identifier-completion-table)
(xref-backend-identifier-completion-ignore-case)
(xref-backend-definitions)(xref-backend-apropos): Adhere to the new rule.
* test/lisp/emacs-lisp/checkdoc-tests.el
(checkdoc-cl-defmethod-with-types-ok)
(checkdoc-cl-defmethod-qualified-ok)
(checkdoc-cl-defmethod-with-extra-qualifier-ok): Adhere to the new rule.

* etc/NEWS: Describe the change.