Use lexical-binding in all of `lisp/emacs-lisp`

Use lexical-binding in all of `lisp/emacs-lisp`

* lisp/emacs-lisp/bindat.el: Use lexical-binding.
(bindat--unpack-group, bindat--length-group, bindat--pack-group):
Declare `last` and `tag` as dyn-scoped.
(bindat-unpack, bindat-pack): Bind `bindat-raw` and `bindat-idx` via
`let` rather than via the formal arglist.

* lisp/emacs-lisp/package-x.el:
* lisp/emacs-lisp/generic.el:
* lisp/emacs-lisp/eieio-opt.el:
* lisp/emacs-lisp/derived.el:
* lisp/emacs-lisp/crm.el: Use lexical-binding.

* lisp/emacs-lisp/helper.el: Use lexical-binding.
(Helper-help-map): Move initialization into declaration.

* lisp/emacs-lisp/regi.el: Use lexical-binding.
(regi-interpret): Remove unused var `tstart`.
Declare `curframe`, `curentry` and `curline` as dyn-scoped.

* lisp/emacs-lisp/shadow.el: Use lexical-binding.
(load-path-shadows-find): Remove unused var `file`.
Tighten a regexp, use `push`.

* lisp/emacs-lisp/tcover-ses.el: Use lexical-binding.  Require `ses`.
Remove correspondingly redundant declarations.
(ses--curcell-overlay): Declare.
(ses-exercise): Use `dlet` and use a properly-prefixed var name.
Fix name of `curcell-overlay` variable.

* lisp/emacs-lisp/unsafep.el: Use lexical-binding.
(unsafep): Bind `unsafep-vars` via `let` rather than via the formal arglist.