Strip EOL characters from wxStyledTextCtrl::GetLineText() return value.

For consistency with all the other wxTextCtrl-like classes, the value returned
by this method must not include line terminator characters (like '\n'). Notice
that Scintilla-specific GetLine() does still include them, for consistency
with the Scintilla API itself.

Closes #13646.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73140 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775