[llvm] [mlir] [mlir][core] Add an MLIR "pattern catalog" generator (PR #146228)

[Maksim Levental via llvm-commits]

makslevental wrote:

I support this with every fiber of my being! Bravo. 

My only comment (aside from `getDebugName`) is that it shouldn't mess with the filesystem and it should just dump to the screen. If you put the impl into it's own cpp file and then do `
#define DEBUG_TYPE "pattern-catalog"`, then people will be able to produce the catalog by just doing `debug-only=pattern-catalog` and piping (eg to a file on disk or whatever).

https://github.com/llvm/llvm-project/pull/146228