This is very similar to the existing mbstring.regex_stack_limit,
but for backtracking. The default value matches pcre.backtrack_limit.
Only used on libonig >= 2.8.0.

By introducing a hook that is called whenever one of
internal_encoding / input_encoding / output_encoding changes, so
that mbstring can adjust it's internal state.

This also makes internal_encoding work with zend multibyte.

* PHP-7.3:
  Update NEWS & UPGRADING
  Add fallbacks for older oniguruma versions
  Add mbstring.regex_stack_limit to php.ini-*
  Implement RF bug #72777 - ensure stack limits on mbstring functions.

The patch creates new config: mbstring.regex_stack_limit, which
defaults to 100000.

RFC: https://wiki.php.net/rfc/mb_str_split

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.

Reported by legale.

Saves us a string duplication, as well as case-insensitive string
comparisons for the likely case of an interned string encoding.

The $Id$ keywords were used in Subversion where they can be substituted
with filename, last revision number change, last changed date, and last
user who changed it.

In Git this functionality is different and can be done with Git attribute
ident. These need to be defined manually for each file in the
.gitattributes file and are afterwards replaced with 40-character
hexadecimal blob object name which is based only on the particular file
contents.

This patch simplifies handling of $Id$ keywords by removing them since
they are not used anymore.