QFontConfigDatabase: Minor code clean-up

Get rid of duplicated includes, useless defines, and private enums
that just duplicate a public ones; avoid variable names collisions.

Change-Id: I540e812b6cd510eb1ed441d97e9af377611d804a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Implement QFontEngine::harfbuzzFont/Face() with HarfBuzz-NG

Change-Id: I5d4fed66d66e8aa650fe181e61dcc2345f0f907a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Decrease code duplication in QFontDatabase-s

Move scriptRequiresOpenType() body right into QFontEngine::supportsScript(),
thus centralizing use of this performance cheat.

Change-Id: I5f494b086f8f900b631c491f41e9cb800002c0f6
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Warn if OpenType support missing for script of interest

Change-Id: I076cfc5244ca3c060fd005cc3fbf30b357604bc7
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>