[MLIR] Let AttrTypeReplacer prefer def builders (NFC)

[gysit]

This commit modifies the AttrTypeReplacer to prefer the default builders when creating attributes or types, avoiding the risk of failures associated with implicit casting. Previously, custom builders could lead to segfaults if a null StringAttr was automatically converted to a StringRef. By preferring the default builder, we avoid these potentially fatal conversions.

[gysit]

This issue came up in the context of #87295.

The AttrTypeReplacer may call the custom builder of attributes such as:

def LLVM_DISubprogramAttr : LLVM_Attr<"DISubprogram", "di_subprogram",
                                      /*traits=*/[], "DIScopeAttr"> {
  let parameters = (ins
    OptionalParameter<"DistinctAttr">:$id,
    OptionalParameter<"DICompileUnitAttr">:$compileUnit,
    "DIScopeAttr":$scope,
    OptionalParameter<"StringAttr">:$name,
    OptionalParameter<"StringAttr">:$linkageName,
    "DIFileAttr":$file,
    OptionalParameter<"unsigned">:$line,
    OptionalParameter<"unsigned">:$scopeLine,
    OptionalParameter<"DISubprogramFlags">:$subprogramFlags,
    OptionalParameter<"DISubroutineTypeAttr">:$type
  );
  let builders = [
    AttrBuilderWithInferredContext<(ins
      "DistinctAttr":$id, "DICompileUnitAttr":$compileUnit,
      "DIScopeAttr":$scope, "StringRef":$name, "StringRef":$linkageName,
      "DIFileAttr":$file, "unsigned":$line, "unsigned":$scopeLine,
      "DISubprogramFlags":$subprogramFlags, "DISubroutineTypeAttr":$type
    ), [{
      MLIRContext *ctx = file.getContext();
      return $_get(ctx, id, compileUnit, scope, StringAttr::get(ctx, name),
                   StringAttr::get(ctx, linkageName), file, line,
                   scopeLine, subprogramFlags, type);
    }]>
  ];

  let assemblyFormat = "`<` struct(params) `>`";
}

This is problematic since the name parameter is optional and hence can be nullptr. The custom builder is called since the StringAttr supports implicit conversion to a StringRef which is fatal in this case since we may try to convert a nullptr.