[C#] Added ToSizedArrayPadded(int padLeft, int padRight) to ByteBuffers to avoid unnecessary copying.

[petersvp]

I've added 2 new functions to C#'s ByteBuffers:
public byte[] ToSizedArrayPadded(int padLeft, int padRight)
public T[] ToArrayPadded<T>(int pos, int len, int padLeft, int padRight)

I needed those to create byte buffers with room in front of them where i can hotwire a header containing the type info and/on package length for TCP Framing.

Code that calls .ToSizedArray only to create new byte array and yet another copy to add some padding wasn't the best approach, so I decided to add the padding feature in the library itself. This is great for highly optimized networking.
My old framing code was the bottleneck because of Buffer.BlockCopy that is after a Buffer.BlockCopy during the .ToSizedArray()

Consider adding something similar to other languages thay may need padding during their framing / similar use cases, where ToSizedArray is THE thing that creates the initial byte array.

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[bjornharrtell]

@aardappel consider merge