[mlir][Linalg] Insert static buffers as high as possible during ComprehensiveBufferization.

This revision allows hoisting static alloc/dealloc pairs as high as possible during ComprehensiveBufferization.
This also aligns such allocated buffers to 128B by default.

This change exhibited some issues wrt insertion points and a missing copy that are also fixed in this revision; tests are updated accordingly.

Differential Revision: https://reviews.llvm.org/D109684