Adding support for getting standard directory paths and provide vfs for them on Apple devices

[soywiz]

We can also provide support for other platforms.

Relevant links:

• https://stackoverflow.com/questions/35439491/ios-cant-get-content-of-caches-directory
• https://developer.apple.com/documentation/foundation/1414224-nssearchpathfordirectoriesindoma?language=objc
• https://developer.apple.com/documentation/foundation/nssearchpathdirectory?language=objc

[soywiz]

Move this to StandardDirectories.getSettingsFolder(gameId: String) or something like that.

val realSettingsFolder: String by lazy {
    when {
        settingsFolder != null -> settingsFolder!!
        else -> when {
            OS.isMac -> "/Users/${Environment["USER"]}/Library/Preferences/$gameIdFolder"
            OS.isWindows -> "${Environment["APPDATA"]}/$gameIdFolder"
            else -> "${Environment["HOME"]}/.config/$gameIdFolder"
        }
    }