Start sharing common code between DeleteContents of ScViewFunc/ScDocFunc.

The goal is to have ScViewFunc::DeleteContents() simply call
ScDocFunc::DeleteContents() while doing the view only stuff in the ScViewFunc
variant.  This is just a step toward that goal.

Change-Id: I2e574f9eb2b2be5340dbfb6f10739dfc2406faae
Share undo doc creation code.

Change-Id: I55f27b61637ba0284479c63c2fa48b0bd8938c0f
Move this one to a common place too.

Change-Id: I7f4e007cfc861dc323b42be353c6ba11091e8fa1