Headers of libui is moved to the local directory

This makes clients of libui to be compiled without depending on global
headers.

Bug: 37731063
Test: sailfish build and boots
Test: 'BOARD_VNDK_VERSION=current m libui' successful
Change-Id: I6546f57964f2103bf3534fb8266fee4fb7d4678a
Merged-In: I6546f57964f2103bf3534fb8266fee4fb7d4678a
22 files changed