Gets keyboard layout info from user space when available.

The layout info consists of a BCP 47 conformant language tag and a
layout type such as "qwerty" or "azerty". They will be used to
initialize the input device.

This is currently used by uinput virtual keyboard to pass in layout
information.

Bug: 237537306
Test: atest inputflinger_tests
Change-Id: Icfc30f1afb0f88dd704d1d598d62a300a032b0f5