[mlir:PDL] Adjust the assembly format for AttributeOp to avoid conflicts with DictionaryAttr

[rriddle]

Summary

Switch the attribute creation operations to use attr-dict-with-
keyword to avoid conflicts (in the case of pdl.attribute) and
confusion(in the case of pdl_interp.create_attribute) with
having a DictionaryAttr as a value and specifying the
attributes of the operation itself (as a dictionary).

Depends On D114814

[jpienaar]

Nit: reflow patch summary on submit

mlir/include/mlir/Dialect/PDL/IR/PDLOps.td

let description = [{
     // Define an attribute with a constant value:
     %attr = pdl.attribute "hello"
     ```
   }];
 
   let arguments = (ins Optional<PDL_Type>:$type,
                        OptionalAttr<AnyAttr>:$value);
   let results = (outs PDL_Attribute:$attr);
-  let assemblyFormat = "attr-dict (`:` $type^)? ($value^)?";
+  let assemblyFormat = "(`:` $type^)? ($value^)? attr-dict-with-keyword";
 
   let builders = [
     OpBuilder<(ins CArg<"Value", "Value()">:$type), [{
       build($_builder, $_state, $_builder.getType<AttributeType>(), type,
             Attribute());
     }]>,
     OpBuilder<(ins "Attribute":$attr), [{
       build($_builder, $_state, $_builder.getType<AttributeType>(), Value(), attr);

mlir/include/mlir/Dialect/PDLInterp/IR/PDLInterpOps.td

let description = [{
 
     ```mlir
     %attr = pdl_interp.create_attribute 10 : i64
     ```
   }];
 
   let arguments = (ins AnyAttr:$value);
   let results = (outs PDL_Attribute:$attribute);
-  let assemblyFormat = "$value attr-dict";
+  let assemblyFormat = "$value attr-dict-with-keyword";
 
   let builders = [
     OpBuilder<(ins "Attribute":$value), [{
       build($_builder, $_state, $_builder.getType<pdl::AttributeType>(), value);
     }]>];
 }
 
 //===----------------------------------------------------------------------===//

mlir/test/Dialect/PDL/ops.mlir

 // -----
 
 pdl.pattern @apply_rewrite_with_no_results : benefit(1) {
   %root = pdl.operation
   pdl.rewrite %root {
     pdl.apply_native_rewrite "NativeRewrite"(%root : !pdl.operation)
   }
 }
+
+// -----
+
+pdl.pattern @attribute_with_dict : benefit(1) {
+  %root = pdl.operation
+  pdl.rewrite %root {
+    %attr = pdl.attribute {some_unit_attr} attributes {pdl.special_attribute}
+    pdl.apply_native_rewrite "NativeRewrite"(%attr : !pdl.attribute)
+  }
+}