Hidden RuntimeHelpers.GetSubArray/String.Substring invocations

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Hidden allocations in C# 11 list patterns:

if (args is ["--help", ..var tail1]) { } // alloc
if (args[0] is ['-', ..var tail2]) { } // alloc

Hidden allocations in slicing expressions:

using System;

_ = args[1..]; // alloc
_ = args[0][1..]; // alloc
_ = args[0].AsSpan()[1..];

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Implemented