Upgrade Kint to 5, stop overriding d() function in favor of new function ddb()

[benvoynick]

The amount of deprecation notices that may be raised by Kint 1.x is getting annoyingly high as of PHP 8.1. Which also means it will straight up stop working some day on new PHP versions.

This PR upgrades to Kint 5. It also makes some other big changes:

• The override of the d() function is removed. In its place is now a non-colliding function ddb() serving the same purpose as the old d(). The README has been updated to note this change. The README is also updated to show that choosing between Debug Bar and inline output is now most easily done by choosing between ddb() (Debug Bar) and d() (inline). This was primarily to allow the next change:
• Kint is now a dependency in composer.json, and will be installed and autoloaded via composer so long as the plugin itself. I am still including a committed copy of Kint inside the plugin, too, which the plugin will fall back to if it does not detect the Kint class. So non-composer-based sites are still supported. Composer-based ones can now have the benefits of Composer, such as being able to upgrade to minor and patch releases of Kint without needing the release of a new version of this plugin.

There are also some other less notable changes, such as type declarations where I thought it would make sense, and adding dump functions to Kint's alias list so that they are omitted from Kint's backtrace output.

Since some of these changes are breaking - plus, the change from Kint 1.x to 5.x - I have also marked the plugin as version 2.0.0 in its PHP file, and would suggest marking a release as such.