Introduce global-eldoc-mode. Move Elisp-specific code to elisp-mode.el.

Introduce global-eldoc-mode.  Move Elisp-specific code to elisp-mode.el.
* lisp/emacs-lisp/eldoc.el (global-eldoc-mode): New minor mode.
(eldoc-schedule-timer): Obey it.
(eldoc-documentation-function): Default to nil.
(eldoc-mode): Don't enable if eldoc-documentation-function is not set.
(eldoc-documentation-function-default, eldoc-get-fnsym-args-string)
(eldoc-highlight-function-argument, eldoc-get-var-docstring)
(eldoc-last-data-store, eldoc-docstring-first-line)
(eldoc-docstring-format-sym-doc, eldoc-fnsym-in-current-sexp)
(eldoc-beginning-of-sexp, eldoc-current-symbol)
(eldoc-function-argstring): Move to elisp-mode.el.
(eldoc-symbol-function): Remove, unused.
* lisp/progmodes/elisp-mode.el: New file.  Rename all "eldoc-*" to "elisp--*".
(elisp-completion-at-point): Rename from lisp-completion-at-point.
(elisp--preceding-sexp): Rename from preceding-sexp.
* lisp/loadup.el: Load new file progmodes/elisp-mode.
* lisp/ielm.el (inferior-emacs-lisp-mode): Set eldoc-documentation-function.
* lisp/emacs-lisp/lisp.el (lisp--local-variables-1, lisp--local-variables)
(lisp--local-variables-completion-table, lisp--expect-function-p)
(lisp--form-quoted-p, lisp--company-doc-buffer)
(lisp--company-doc-string, lisp--company-location)
(lisp-completion-at-point): Move to elisp-mode.el.
* lisp/emacs-lisp/lisp-mode.el (lisp--mode-syntax-table): New syntax-table,
extracted from emacs-lisp-mode-syntax-table.
(emacs-lisp-mode-abbrev-table, emacs-lisp-mode-syntax-table): Move to
elisp-mode.el.
(lisp-imenu-generic-expression): Add comments to document what comes
from which Lisp dialect.
(emacs-lisp-mode-map, emacs-lisp-byte-compile)
(emacs-lisp-byte-compile-and-load, emacs-lisp-mode-hook)
(emacs-lisp-mode, emacs-list-byte-code-comment-re)
(emacs-lisp-byte-code-comment)
(emacs-lisp-byte-code-syntax-propertize, emacs-lisp-byte-code-mode)
(lisp-interaction-mode-map, lisp-interaction-mode)
(eval-print-last-sexp, last-sexp-setup-props)
(last-sexp-toggle-display, prin1-char, preceding-sexp)
(eval-last-sexp-1, eval-last-sexp-print-value)
(eval-last-sexp-fake-value, eval-sexp-add-defvars, eval-last-sexp)
(eval-defun-1, eval-defun-2, eval-defun): Move to elisp-mode.el.
* src/lisp.mk (lisp): Add elisp-mode.elc.