[mlir][NFC] Move and improve ownership-based buffer dellocation docs (#89196)

Move the documentation of the ownership-based buffer deallocation pass
to a separate file. Also improve the documentation a bit and insert a
figure that explains the `bufferization.dealloc` op (copied from the
tutorial at the LLVM Dev Summit 2023).

Author: matthias-springer

mlir/docs/BufferDeallocationInternals.md

@@ -1,5 +1,8 @@
 # Buffer Deallocation - Internals
 
+**Note:** This pass is deprecated. Please use the ownership-based buffer
+deallocation pass instead.
+
 This section covers the internal functionality of the BufferDeallocation
 transformation. The transformation consists of several passes. The main pass
 called BufferDeallocation can be applied via “-buffer-deallocation” on MLIR