Make FontClient::New() for async text load

Make FontClient::New() for async text load

Since we may need to use some new FontClient API that might not
used on EventThread case.

DaliHandle itself can be created at worker thread. So we need to
prepare of this usecase.

TODO : FontClient might not be thread-safe. We need to check it

Change-Id: I768bf48314fb8f66548205744d3df4f19bacefcd
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>