Exporting C headers from system/core

Moved headers from include/libcutils and include/liblog to
libcutils/include and liblog/include respectively, so they can be
exported via these libs. They needed to be moved since Soong does
not allow export from external folder.

Added symlink from old locations. They are needed since Soong
includes system/core/include by default. Once all modules are
cleaned up to explicitly add the required libs, the symlinks will be
removed.

Also added liblog_vndk_headers that exports a special log/log.h for
VNDK.

Moved headers of libcutils to libcutils_headers. They should be used
by modules for header-only inlines. Added libcutils_headers as
dependency of libcutils.

Added libcutils_vndk_headers that exports a special cutils/log.h
deprecating usage of the file. A later CL will deprecate the one in
libcutils_headers

Test: Add above libs to shared lib of local module
Change-Id: I6e1f9c5f23d8b6eae13dc3b7e5dfe7fae93b8510