[PHP] Enum with type integer creates invalid const names

Description

When a model is generated for a schema defined as an enum with type integer a class constant is included for each value. These constants will use the integer value as their name which is not valid PHP. For enums with type string the names for numeric values seem to be prefixed with _ but this does not happen for type integer.

Swagger-codegen version

3.0.30

Swagger declaration file content or url

The following schema definition:

"ResponseCode": {
    "enum": [
        1,
        2
    ],
    "type": "integer",
    "format": "int32"
}

Results in:

class ResponseCode
{
    /**
     * Possible values of this enum
     */
    const 1 = 1;
const 2 = 2;
    /**
     * Gets allowable values of the enum
     * @return string[]
     */
    public static function getAllowableEnumValues()
    {
        return [
            self::1,
self::2,        ];
    }
}

While the following schema definition:

"ResponseCode": {
    "enum": [
        "1",
        "2"
    ],
    "type": "string"
}

Results in:

class ResponseCode
{
    /**
     * Possible values of this enum
     */
    const _1 = '1';
const _2 = '2';
    /**
     * Gets allowable values of the enum
     * @return string[]
     */
    public static function getAllowableEnumValues()
    {
        return [
            self::_1,
self::_2,        ];
    }
}

Reproduce the issue with the integer enum schema and inspect the PHP enum generation path in the template-driven code generator. Compare it with string enum generation; done means generated PHP uses valid constant names while preserving the integer values and allowable-value references.