This commits corrects the calculation of the Frame Node label size,
making it independent of the 'Line Width' user preference.
Since `U.dpi` is actually DPI divided by `U.pixelsize` and `U.pixelsize`
is calculated from line-width multiplying by `U.pixelsize` undoes
the connection between line-width and label size.
It now stays the same, regardless of the line-width setting.
Reviewed By: Julian Eisel, Harley Acheson
Differential Revision: https://developer.blender.org/D14338
c8cef83fae