Add system font configuration file for CJK variable font

// Copies the font configuration file into system/etc for the product as fonts.xml.

// Additional fonts should be installed to /product/fonts/ alongside a corresponding

// fonts_customiztion.xml in /product/etc/

prebuilt_etc {

soong_config_bool_variable {

    name: "use_var_font",

}

soong_config_module_type {

    name: "prebuilt_fonts_xml",

    module_type: "prebuilt_etc",

    config_namespace: "noto_sans_cjk_config",

    bool_variables: ["use_var_font"],

    properties: ["src"],

}

prebuilt_fonts_xml {

    name: "fonts.xml",

    src: "fonts.xml",

    soong_config_variables: {

        use_var_font: {

            src: "fonts_cjkvf.xml",

        },

    },

}

prebuilt_etc {

prebuilt_fonts_xml {

    name: "font_fallback.xml",

    src: "font_fallback.xml",

    soong_config_variables: {

        use_var_font: {

            src: "font_fallback_cjkvf.xml",

        },

    },

}