Allow automatic text direction in Painter::text()

Allow automatic text direction in Painter::text()

It is wrong to assume that direction is left-to-right when no indication exist.

Add a new enum with values LtR, RtL and Auto to be used as argument of
the private text() methods. When direction is Auto, let Qt decide how
the string shall be layed out.

This is reimplementation of 51ee267c. A direct cherry-pick was not possible.

Fixes bug #10169.