Update `update_compat_info.php` to use PHP_CompatInfo version 3

Summary:
Fixes T5377. The current `scripts/update_compat_info.php` script works for PHP CompatInfo version 2, but doesn't work with the newer version 3.

There are a few breaking changes in version 3 that had to be addressed:

- PHP 5.3 is required. Whilst Arcanist is generally compatible with PHP 5.2, I don't think that having this dependency presents any real issues because it is purely a development tool that is rarely updated.
- [[https://getcomposer.org/ | Composer]] is used for packaging, which makes including the library slightly more complicated. Basically, I had to install `PHP_CompatInfo` globally with Composer (`composer global require "bartlett/php-compatinfo"` and then symlink `~/.composer/vendor` into `externals/includes`.

Test Plan: Compared the `resources/php_compat_info.json` file. There are a bunch of functions/classes that //were// in this file but are no longer, but I think that I've covered the most popular extensions.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5377

Differential Revision: https://secure.phabricator.com/D9568