[mlir] GreedyPatternRewriter: fix counting of iterations

The GreedyPatternRewriteDriver did previously not count the first iteration. I.e., when setting `config.maxIterations = 1`, two iterations were performed. In pratice, this number is not really important; we usually just need a limit in some reasonable order of magnitude. However, this fix allows us to write better convergence/worklist tests with carefully crafted test patterns to purposely trigger edge cases in the driver.

Similarly, the first rewrite was previously not counted towards `config.maxNumRewrites`.

For consistency, `OpPatternRewriteDriver` now uses `config.maxNumRewrites` instead of `config.maxIterations`; this driver does not have "iterations", it consists of a single loop (corresponding to the inner loop in the GreedyPatternRewriteDriver).

Differential Revision: https://reviews.llvm.org/D141365