[valid-describe] Support functions as 'name' argument

Since Jest 22 describe() also allows function references as “name” (instead of a string).

See https://github.com/facebook/jest/pull/5154.

See also the TS typing: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/f79c08624659aea629bf0d1dc2f30a15e2c68383/types/jest/index.d.ts#L390

This is not supported by valid-describe:

function calc() { /* ... */ }

describe(calc, () => {
    it("adds up two values", () => {
        // ...
    });
});

=> Emits “error First argument must be name jest/valid-describe”.

[garyking]

I would just say to give us an option on the rule, to disable checking the name field, since this rule also does other checks as well.

[G-Rath]

FYI I’m going to be moving this into valid-title, just b/c of code structure.

From everything I can tell, only describe supports names that are not string, so valid-title will handle checking the title, but have an ignoreTypeOfDescribeName option that should solve this 😃