Add ZipMap

[DanOpcode]

Implementation of ZipMap proposed in #661.

[viceroypenguin]

FYI: This operator has been included in SuperLinq 4.0.0, which has now been published.

[atifaziz]

@matachi Thanks for contributing this and sorry for having taken so long to get back with a review. Usually, I don't pay attention to a new PR unless the CI build errors are fixed. Anyway, since master had moved on considerably since this PR was opened, I've aligned it with a merge and added my review. Hope you'll find the time to address the comments soon.

[atifaziz]

I think the first tuple element should be named Source or Input instead of Item. Thoughts?

[atifaziz]

The NullArgumentTest tests are breaking. The fix is to validate the arguments eagerly and wrap the iterator in a local function as follows (otherwise arguments are validated when the sequence is iterated rather than when ZipMap is called):

Suggested change

	foreach (var item in source)
	{
	yield return (item, func(item));
	}
	return _(); IEnumerable<(TSource, TResult)> _()
	{
	foreach (var item in source)
	{
	yield return (item, func(item));
	}
	}