Enable Contact(vCard) and Calendar Events sharing, differentiate between file and plain text shares

[jeffersondarcy]

added support for receiving vCards and calendar events
added differentiator isFile, because there is no other way to find out if text was shared plain or via file

please squash merge, because I had to revert som commits from our fork

[jeffersondarcy]

@lgl-fengwang thanks for approving the PR, do you know if it will be merged soon?

[mcfriend99]

Why is this not yet merged??

[mostafasany]

Can we approve this

[alcampospalacios]

This would merge soon?

[khokholikov]

Hello, @jeffersondarcy. Thank you for your efforts!

I came across your PR because for me too it is a problem that one cannot differentiate between plain text and text files. Although I think that the fix should be made in a general way, not differentiating between vCards and calendar events and all other text files. For instance, when one shares .log, .md, .js or any other programming language files (which is useful if you use the share activity to pass an attachment which can be literally any file) the plugin does anything. I found with the debugger that it handles somehow the text but the example given in https://github.com/KasemJaffer/receive_sharing_intent/blob/master/example/lib/main.dart doesn't process the shared text and just prints an empty result, although this is another question which I can explore by myself.

The question here is wether you do agree that it should handle ANY types of text files as files, NOT JUST vCards and calendar events. If yes, how is it best to do: if I try to edit your code or if you can supplement it yourself? For now I am new to PR functionality and I don't know if I can edit another user's PR or not.

Yes, forgot to tell that I have tested only on iOS as for now.