FIX: ensures insert hyperlink works with mailto (PR #10867)

This commit also renames an incorrectly named test and uses https as default instead of http, in 2020 it’s reasonnable to think we most likely want https and not http. User can still specify http if required.

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Could I convince you to test for url.indexOf("mailto:") !== 0 instead since “http://foo.com/mailto:something/” is a valid URL?

I’m fine with this :+1:

I decided to move this fn to lib:url and added more tests for this