Add project-local editorconfig to silence warnings about intentional stuff

Analyzers/Terminal.Gui.Analyzers.Internal.Tests/.editorconfig

@@ -0,0 +1,8 @@
+# CA1707: Identifiers should not contain underscores
+dotnet_diagnostic.CA1707.severity = none
+
+#CA1711:Identifiers should not have incorrect suffix
+dotnet_diagnostic.CA1711.severity = none
+
+# RCS1154:Sort enum members
+dotnet_diagnostic.RCS1154.severity = none