StdLibUefi

This is a fixed-up version of edk2's StdLib/LibC/Uefi.

NOTE: StdExtLib, StdLibDevConsole, StdLibInteractiveIO and StdLibUefi all go together.

Differences:

• ^D is the VEOF character, allowing to break out of input.
• Termios init is moved to StdLibDevConsole, where it belongs.
• getopt is now in StdExtLib (sharing the backing implementation for getopt_long).