Pods conflict with Markdown loader

Pods uses the base Markdown PHP project, while Jetpack uses Markdown + Extra. The current class exists check only checks the extra-specific class.

https://github.com/Automattic/jetpack/blob/master/_inc/lib/markdown/0-load.php

`if ( ! class_exists( 'MarkdownExtra_Parser' ) )`

However, the code inside of extra.php doesn't check if the 'Markdown' function exists yet, or some of the other things already defined/declared like constant(s).

How best should we proceed? Pods loads Markdown before Jetpack, but Jetpack needs Markdown+Extra.

Start by tracing the Markdown loading logic in _inc/lib/markdown/0-load.php and the referenced extra.php, including the existing class, function, and constant checks. Reproduce the load order where Pods loads base Markdown before Jetpack, then define done as Jetpack loading Markdown+Extra without redeclaration or compatibility conflicts.

Written by the indexing model from the issue text.