System.Reflection.Metadata throws BadImageFormatException on bad input

If a user passes in a bad handle, for instance they get an `ExportedTypeHandle` from one MetadataReader instance's `MetadataReader.ExportedTypes`, and pass it to a different MetadataReader instance via `MetadataReader.GetExportedType` we will throw `BadImageFormatException`. This is unintuitive since both images are fine and the problem was with the *argument* passed to `GetExportedType`. We should probably be throwing something derived from `ArgumentException`, like `ArgumentOutOfRangeException` or something similar.

/cc @nguerrera @tmat