Closes GH-4218.

Normalization include:
- Use dnl for everything that can be ommitted when configure is built in
  favor of the shell comment character # which is visible in the output.
- Line length normalized to 80 columns
- Dots for most of the one line sentences
- Macro definitions include similar pattern header comments now

The Autoconf's default AS_HELP_STRING macro can properly format help
strings [1] so watching out if columns are aligned manually is not
anymore.

[1] https://www.gnu.org/software/autoconf/manual/autoconf.html#Pretty-Help-Strings

This patch removes the so called local variables defined per
file basis for certain editors to properly show tab width, and
similar settings. These are mainly used by Vim and Emacs editors
yet with recent changes the once working definitions don't work
anymore in Vim without custom plugins or additional configuration.
Neither are these settings synced across the PHP code base.

A simpler and better approach is EditorConfig and fixing code
using some code style fixing tools in the future instead.

This patch also removes the so called modelines for Vim. Modelines
allow Vim editor specifically to set some editor configuration such as
syntax highlighting, indentation style and tab width to be set in the
first line or the last 5 lines per file basis. Since the php test
files have syntax highlighting already set in most editors properly and
EditorConfig takes care of the indentation settings, this patch removes
these as well for the Vim 6.0 and newer versions.

With the removal of local variables for certain editors such as
Emacs and Vim, the footer is also probably not needed anymore when
creating extensions using ext_skel.php script.

Additionally, Vim modelines for setting php syntax and some editor
settings has been removed from some *.phpt files.  All these are
mostly not relevant for phpt files neither work properly in the
middle of the file.

skeleton can still be leveraged with older PHP releases, including
PHP 7.2.

I wanted to add this capability since PHP 7.2 is still widely provided
with most Linux distributions.

I am using ext_skel.php on a vanilla Ubuntu 18.04 and Windows
in order to illustrate how to develop a PHP extension for both
OS using the default tools provided by the distributions.
  see: https://github.com/vjardin/php-bonjour

* PHP-7.2:
  [ci skip] Update NEWS
  [ci skip] Update NEWS
  Fix #77035: The phpize and ./configure create redundant .deps file