[BUG] [Swift] Number without specified type doesn't set x-swift-optional-scalar to true

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

I need to generate obj-c accessible models and there is a problem in interoperability with some nullable types which cannot be represented in obj-c. Swift5ClientCodegen does support that but there is a problem if in OpenAPI declaration is missing format and only specify type. Then it's generated into Double? but postProcessModelProperty function does not trigger x-swift-optional-scalar to true. It can definitely be fixed on declaration side but client Codegen should expected it, too.

    @Override
    public void postProcessModelProperty(CodegenModel model, CodegenProperty property) {
        super.postProcessModelProperty(model, property);

        boolean isSwiftScalarType = property.isInteger || property.isLong || property.isFloat
                || property.isDouble || property.isBoolean;
        if ((!property.required || property.isNullable) && isSwiftScalarType) {
            // Optional scalar types like Int?, Int64?, Float?, Double?, and Bool?
            // do not translate to Objective-C. So we want to flag those
            // properties in case we want to put special code in the templates
            // which provide Objective-C compatibility.
            property.vendorExtensions.put("x-swift-optional-scalar", true);
        }
    }

openapi-generator version

4.3.1

OpenAPI declaration file content or url

    "GpsCoordinatesTO": {
      "type": "object",
      "properties": {
        "gpsX": {
          "type": "number",
          "format": "double"
        },
        "gpsY": {
          "type": "number"
        }
      },
      "title": "GpsCoordinatesTO"
    }

-->

Command line used for generation

openapi-generator generate -i swagger.json -g swift5 --additional-properties=library=urlsession,objcCompatible=true -o swift/ --skip-validate-spec

Steps to reproduce

Generate client from declaration which includes snippet above.

Suggest a fix

Update postProcessModelProperty function to handle only number because it's generated into Swift as Double? which cannot be represented in obj-c.

Start at Swift5ClientCodegen.postProcessModelProperty and reproduce the issue with the provided OpenAPI declaration and swift5 generation command. Confirm that a number without a format generates as Double? and that x-swift-optional-scalar is set, then verify the resulting Objective-C-compatible output with the relevant generator checks.