[mlir][linalg][bufferize][NFC] Analyze OpOperands instead of OpResults

With this change, the analysis takes a look at OpOperands instead of OpResults. OpOperands can bufferize out-of-place (even if they have no aliasing OpResults). The analysis does no longer care about OpResults.

Previously, only OpResults could bufferize out-of-place, so OpOperands that have no aliasing OpResults were never copied by Comprehensive Bufferize. This does not fit wwell with the new CallOp bufferization that is introduced in a subsequent change. In essence, called FuncOps can then be treated as "black boxes" that may read/write to any bbArg, even if they do not return anything.

Differential Revision: https://reviews.llvm.org/D115706