Finish converting unit test suites to shared suite

This PR finishes the works started in #42 and moves all tests for the FSP events into a generic top-level unit test suite that can be imported by every provider.

Before this can be merged, some bugs need to be fixed. For example, as described in #8, the WebDAV client does not return the correct size of a file in the metadata call, so the shared test breaks for it.

Closes #18
Because to check every character you either need a 512 character long hardcoded test string to compare it to, which is hard to edit (counting characters manually), or you have to programmatically generate such a string, which is bad because you don't want too much logic in the tests. So I chose this.

As for the string check, that just ensures that the conversion happened correctly. I guess that should really be a separate test case for `arrayBufferToString` though