Tweak the default wxApp::GetAppDisplayName() logic.

Tweak the default wxApp::GetAppDisplayName() logic.

Don't capitalize the app name if it had been explicitly set with SetAppName()
as this can result in unexpectedly wrong value. Do capitalize the program name
which is used as app name by default and don't store the program name in
m_appName to be able to distinguish between the two cases.

Closes #11165.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61821 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775