* src/keymap.c (Fhelp__describe_vector):
* lisp/help.el (describe-map): Use Lisp versions of describe_command
and describe_translation.
* src/keymap.c (describe_command, describe_translation): Remove.
(describe_vector_basic): New function.

The previous conversion of describe_vector from C to Lisp for the
keymap and char table case lead to an unacceptable performance hit.
Moving back to the C version, as we do here, makes this function
around 50 times faster.

The Lisp version of `substitute-command-keys' was benchmarked using
the form `(documentation 'dired-mode)', which now takes less than 8 ms
on my machine.  This is around 16 times slower than the previous C
version.

Thanks to Stefan Monnier for helpful pointers on benchmarking.

* src/keymap.c (Fhelp__describe_vector): New defun to expose
describe_vector to Lisp for keymaps and char tables.
(syms_of_keymap): New defsubr for Fhelp__describe_vector.
* lisp/help.el (describe-map): Use above defun instead of Lisp
version.
(help--describe-vector): Remove defun; keep it commented out for now.

* lisp/help.el (help--describe-vector): New Lisp implementation of
describe_vector.
* src/keymap.c (Fdescribe_vector_internal): Remove defun.
(syms_of_keymap): Remove defsubr for Fdescribe_vector_internal.

Third step in converting substitute-command-keys to Lisp.

* lisp/help.el (describe-map): New Lisp version of describe_map.
(help--describe-map-compare, help--describe-translation)
(help--describe-command, help--shadow-lookup): New helper
functions for describe-map.
(help--keymaps-seen, help--previous-description-column): New
variables.
* src/keymap.c
(Fkeymap__get_keyelt): New defun to expose get_keyelt to Lisp.
(Fdescribe_map_tree_old, Fdescribe_map): Remove defuns.
(Fdescribe_vector_internal): New defun to expose describe_vector to
Lisp in a way usable by describe-map.
(syms_of_keymap): New defsubrs for Fkeymap__get_keyelt and
Fdescribe_vector_internal.  Remove defsubrs for Fdescribe_map_tree_old
and Fdescribe_map.  Remove 'help--keymaps-seen'.

* test/lisp/help-tests.el
(help-tests-substitute-command-keys/shadow): Extend test.
(help-tests-substitute-command-keys/test-mode)
(help-tests-substitute-command-keys/compare-all)
(help-tests-describe-map-tree/no-menu-t)
(help-tests-describe-map-tree/no-menu-nil)
(help-tests-describe-map-tree/mention-shadow-t)
(help-tests-describe-map-tree/mention-shadow-nil)
(help-tests-describe-map-tree/partial-t)
(help-tests-describe-map-tree/partial-nil): New tests.

This is the second step in converting substitute-command-keys to Lisp.

* lisp/help.el (describe-map-tree): New Lisp version of
describe_map_tree.
(substitute-command-keys): Update to use above function.
* src/keymap.c (Fdescribe_map): New defun to expose describe_map to
Lisp.
* src/keymap.c (syms_of_keymap): New variable 'help--keymaps-seen'; a
temporary kludge planned for removal.  New defsubr for Fdescribe_map.

This is only the first step towards a full Lisp implementation, and
does not remove the old C code.  On the contrary, it is partly based
on using the old C code, which is to be replaced in steps.  This also
makes it easy to test that it produces the same output as the old.

* src/doc.c (Fsubstitute_command_keys_old): Rename from
Fsubstitute_command_keys.
(Fget_quoting_style): New defun to expose text_quoting_style to Lisp.
(syms_of_doc): Expose above symbols.
* lisp/help.el (substitute-command-keys): New Lisp version of
substitute-command-keys.  (Bug#8951)

* src/keymap.c
(Fdescribe_map_tree): New defun to expose describe_map_tree to Lisp.
(syms_of_keymap): New defsubr for Fdescribe_map_tree.

* src/keyboard.c (help_echo_substitute_command_keys):
* src/doc.c (Fdocumentation, Fdocumentation_property):
* src/print.c (print_error_message):
* src/syntax.c (Finternal_describe_syntax_value): Fix calls to use new
Lisp implementation of substitute-command-keys.

* test/src/doc-tests.el: Remove file.
* test/lisp/help-tests.el: Add tests for substitute-command-keys
copied from above file.

* lisp/gnus/smiley.el (smiley-region): Use text properties for the
emojis instead of rewriting the message.

* lisp/gnus/smiley.el (smiley-style): Add emoji
tag.
(smiley-emoji-regexp-alist): New defcustom.
(smiley-update-cache, smiley-region): Support emoji (non-image)
replacement (bug#43889).

* lisp/nxml/nxml-mode.el (nxml-newline-and-indent): Make argument
optional to conform to 'comment-line-break-function'.  (Bug#40193)