Adds more locale specific settings to the DateFormatter to support wider ranges of default system locales. If the application containing the server would declare support for other locales (such as deDE or plPL) or the default system locale wouldn't be compatible with enUS making the RFC1123 formatted string non RFC compliant. This fix makes sure that the formatter always uses the enUS_POSIX locale and the Georgian calendar.
Example
The returned string with default locale set as deDE is Don, 05 Dez 2019 19:27:05 GMT instead of Thu, 05 Dec 2019 19:27:05 GMT making the first string non RFC compliant.