Add a utility script to auto-generate CHECK commands for mlir test cases.

This script is a utility to add FileCheck patterns to an mlir file. The script will heuristically insert CHECK/CHECK-LABEL commands for each line within the file. By default this script will also try to insert string substitution blocks for all SSA value names. The script is designed to make adding checks to a test case fast, it is *not* designed to be authoritative about what constitutes a good test!

Note: Some cases may not be handled well, e.g. operands to operations with regions, but this script is only intended to be a starting point.

Example usage:
$ generate-test-checks.py foo.mlir
$ mlir-opt foo.mlir -transformation | generate-test-checks.py

module {
  func @fold_extract_element(%arg0: index) -> (f32, f16, f16, i32) {
    %cst = constant 4.500000e+00 : f32
    %cst_0 = constant -2.000000e+00 : f16
    %cst_1 = constant 0.000000e+00 : f16
    %c64_i32 = constant 64 : i32
    return %cst, %cst_0, %cst_1, %c64_i32 : f32, f16, f16, i32
  }
}

// CHECK-LABEL:   func @fold_extract_element(
// CHECK-SAME:                               [[VAL_0:%.*]]: index) -> (f32, f16, f16, i32) {
// CHECK:           [[VAL_1:%.*]] = constant 4.500000e+00 : f32
// CHECK:           [[VAL_2:%.*]] = constant -2.000000e+00 : f16
// CHECK:           [[VAL_3:%.*]] = constant 0.000000e+00 : f16
// CHECK:           [[VAL_4:%.*]] = constant 64 : i32
// CHECK:           return [[VAL_1]], [[VAL_2]], [[VAL_3]], [[VAL_4]] : f32, f16, f16, i32
// CHECK:         }

PiperOrigin-RevId: 263242983