Text vertex shader is incorrect leading to pixelated rendering with non-integer scaling

When using non-integer screen scaling, QtQuick NativeRendering results in blurry or pixelated text. See also QTBUG-67007

I traced it down to the textmask.vert shader file which tries to align it to the pixel grid by rounding. However, it ends up rounding incorrectly for non-integer dpr values. I am not a shader expert so I cannot tell you what exactly went wrong, I only noticed that not rounding and dividing by dpr "fixes" the issue but will re-introduce a bug that was fixed by doing this.

The offending line is

gl_Position = matrix * floor(vCoord * dpr + 0.5) / dpr;

introduced in 6e883c535b91c55289d54aa639199ca0a4decaec

The same issue is present in the outlinedtext.vert (where it was forgotten in C++ code to set the dpr uniform but this is a separate issue )