(LTS) Add option to store colors as hex

[ninjaguardian]

Adds this option to GsonConfigSerializerBuilder:

    /**
     * If disabled, writes colors to the json in decimal ({@code -1610612736}).
     * If enabled with JSON5 ({@link #setJson5(boolean)}), writes colors to the json as hexadecimal literals ({@code 0xA0000000}).
     * If enabled without JSON5, writes colors to the json as hexadecimal strings ({@code "0xA0000000"}).
     * Colors are saved in ARGB.
     *
     * @param hexColor whether to store color in hexadecimal instead of decimal
     * @return this builder
     */
    GsonConfigSerializerBuilder<T> setStoreColorsAsHex(boolean hexColor);

Main: #356