Drastically simplify using Composer Runtime API (v2)

[webflo]

Related to https://github.com/webflo/drupal-finder/pull/64

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• Make DrupalFinder class as deprecated
• New class DrupalFinderComposerRuntime (please provide better names for this class)
• Keeps tests for both classes

@weitzman Please review. This should work for drush. You could bump the required version to 1.3.0. Its not a new major version. Should work with mglaman/phpstan-drupal too.

Packagist has a list of dependent packages: https://packagist.org/packages/webflo/drupal-finder/dependents?order_by=downloads

[weitzman]

I'm fine with the new DrupalFinderComposerRuntime() class. I would have gone for the backward compat break in a 2.x release but this way is fine too.