Implement generic methods on arrays

[jp2masa]

From @jp2masa on February 21, 2017 19:19

Currently we don't handle generic methods on arrays.
Example:

IEnumerable<string> xEnumerable;
string[] xArray = new string[] { "a", "b", "c" };
xEnumerable = xArray;
xEnumerable.GetEnumerator();

This code won't work, because Array doesn't have an implementation for this method. Array can be used as ICollection<T>, IEnumerable<T> and IList<T>
The implementations for these interfaces are in System.SZArrayHelper, but the compiler needs an implementation that replaces calls to the generic method on arrays with calls to the methods in SZArrayHelper.

Copied from original issue: CosmosOS/Cosmos#583

[fanoI]

We can take inspiration from what has been done in CoreRT and implement explicitely Array<T>:
https://github.com/dotnet/corert/blob/master/src/System.Private.CoreLib/src/System/Array.CoreRT.cs#L1428

I think this is the other piece that make this working seamless:
https://github.com/dotnet/corert/blob/master/src/Runtime.Base/src/System/Array.cs#L47