PluralRules should have a test for parsing all rules

[zbraniecki]

In #230 I'm moving PluralRules to DataProvider and in the process I'm removing a test that was testing all rules because I don't want to land all of them in test data of the crate.

Instead, once we settle on the location of all parsed data, we should re-add the test with that location.

(I'm also not sure if DataProvider exposes a way to get all available locales, but if it doesn't that would be a blocker).

[sffc]

Related: #227

(I'm also not sure if DataProvider exposes a way to get all available locales, but if it doesn't that would be a blocker).

It can as long as the DataProvider also implements DataEntryCollection. CldrJsonDataProvider implements it. FsDataProvider doesn't yet implement it, but an implementation would be as trivial as a crawl over the files in the directory.