Allow using the letter 'E' (capital) as a symbol of exponent when entering floating point numbers.

Currently, only the letter 'e' is accepted when editing wxPG numeric properties.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78156 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775