All keyboard shortcuts

I'm not aware of anything like this, but what I've been doing is using the functionality to see the actions bound to a particular key. This is fairly well hidden - in the Keymap settings, at the top right between the search box and the trash can is an icon that you can click to get a popup allowing you to test keys. Unfortunately this isn't much good for testing combinations across different platforms though. One of the JetBrains guys told me that the best strategy is to ship your plugin without shortcuts assigned and remind people to assign them when they install, otherwise avoiding conflicts is pretty difficult.