Add the possibility to inject a ITiffPixelBufferReader to optimize large tile based tiffs

[donin1129]

I encountered a problem encoding a very large tiled image. First there is a performance issue forcing the usage of MemoryBuffer. Second, the MemoryBuffer has max array size that is System.Int32.MaxValue.

In this commit, I added the following:

• Keep ITiffPixelBufferReader as abstract as possible until necessary for a cast.
• Allow injection of IPartialBufferProvider.
• Provide test / example how to use IPartialBufferProvider to optimize the buffer preparation speed.
• All tests run green.