Blurry text with fractional scaling

Using fractional scaling under Wayland occasionally produces squished or stretched glyphs.

The glyphs end up correctly in the glyph cache texture but they are rendered incorrectly by the textmask.vert shader: https://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/scenegraph/shaders_ng/textmask.vert#n25

Removing the rounding fixes the rendering but clearly it has some use on other platforms.

I already reported something similar as QTBUG-70481 back then which was fixed but apparently it’s still not fully resolved.