Revert "Page Breaks: IsLeaveWindow() is unreliable, we do not need it here."
Revert "Page Breaks: IsLeaveWindow() is unreliable, we do not need it here."

This reverts commit 60c968e9a2ef14aa289e677bd7f40d2c4724fd12. This
introduced flickering page break button

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core