Testing Flutter plugin settings

[InMatrix]

The Editor UI Guides setting is turned on by default on the 35.1 plugin or later due to a bug. We should find a way to test code dealing with plugin settings.

[jacob314]

First step is that for manual testing we need a robust way to clear settings on the local machine so we are always sure we are testing relative to a clean IntelliJ setup instead of one where settings have already been modified.

[stevemessick]

The wiki has a description of how to clear cached data to simulate a fresh install. However, I think it is targeting the runtime workbench, not release testing.

What I do before release testing, on a Mac, is delete four directories:
~/Library/{Application\ Support, Caches, Logs, Preferences}/<product-name>
You'll have to re-install the Dart plugin, but you have to install Flutter plugin from disk anyway. (Those directory names, and their non-Mac variants, are detailed on one of the IntelliJ documentation pages.)

Having an integration test to cover at least some of the settings would be good.