[mlir][linalg][bufferize][NFC] Collect equivalent FuncOp BBArgs in PostAnalysisStep

Collect equivalent BBArgs right after the equivalence analysis of the FuncOp and before bufferizing. This is in preparation of decoupling bufferization from aliasInfo.

Also gather equivalence info for CallOps, which was missing in the
previous commit.

Differential Revision: https://reviews.llvm.org/D114847