Meta: Add .mailmap to ascribe git commits to proper author.

From time to time a new commit will appear from an existing commit which has a different name or email address (or both) than an existing name or email address. This occurs because of changing names and changing emails and because of mistakes. Additionally, the `svg`-to-`git` process double-encodes names from `profiles.wordpress.org` causing corruption in names with non-US-ASCII characters.

This patch introduces a `.mailmap` file to alias committers so that:

 - All contributions for a given person are shown for that person.
 - Committers will be able to control or fix the display of their own name.

The `.mailmap` file is a standard `git` configuration.

Developed in https://github.com/wordpress/wordpress-develop/pull/7180
Discussed in https://core.trac.wordpress.org/ticket/61864

Fixes #61864.

Built from https://develop.svn.wordpress.org/trunk@58899


git-svn-id: http://core.svn.wordpress.org/trunk@58295 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-alpha-58898';
+$wp_version = '6.7-alpha-58899';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.