Document layout, export, and Verify improvements

Usability and reliability improvements

Fixed an issue in Verify where task cards could appear with content cut off when viewing information requirements.
Fixed an issue in PDF exports where some linked reference numbers and icons were rendered too large in certain cases.
Improved element linking reliability in Verify by refining underlying rules.
Added new units for datatype IfcConcentrationMeasure, including parts per million (ppm) and parts per billion (ppb).
Improved checkbox behavior in Docs so checkbox size now scales with font size and remains visually centered.
Sections can now be created without a section title, meaning they won’t appear in the index or be printed as a heading.