Changed the auto-seal visitor to change all virtual methods that do not have override to be non-virtual.
    This should handle correctly properties and indexers now, as well as imported types from other assemblies that are not visited.
    It sets accordingly the virtual and override flags, and fixed some several different cases where the override was not correct (generating either compile errors or warnings with incorrectly generated code).
    Added /autoseal_verbosity compiler flag to help debug issues with auto-sealer not working as expected.

As a side note, we also seal classes that are not base class of another class, however it does not seem to generate a different IL.
Once resolved, we will do something similar for the methods to see if it helps further (inline should work as soon as the method is not virtual anymore).