Normalize references to Insert keys #13648 (#16489)
Fixes #13648
Summary of the issue:
The Welcome Screen and User Guide used different terms, "main Insert" and "Extended Insert" respectively, to refer to the same key.
Description of user facing changes
Both the Welcome Screen and User Guide now call Extended/main Insert by simply "Insert."
Description of development approach
Modified wording in userGuide and startupDialogs files, as well as the startup system test that checks the Welcome Screen text.
