Some users still prefer the fake bold look even if in some cases it does
not look good. So add an environment variable -
QT_NO_SYNTHESIZED_BOLD_LIMIT - to allow that fallback to stay in place.
Pick-to: 6.2 5.15
Change-Id: I8212c1fa36edb4730b187dc4a23ea45f94981154
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>