- do not blindly use `FindPage()` / `FindView()` result in `Exception.Message` or returned results
- failure scenarios involve new `Any()` calls but rarely additional `List<string>()` allocations
- change `ViewEngine_ViewNotFound` resource to be consistent with similar errors
- remove trailing period at end of searched locations list
nit: remove remaining `null` checks of `SearchedLocations` in not found cases; never `null` then
- Changing HtmlHelper and HelperResult to implement IHtmlContent.
- Introducing BufferedHtmlContent.
- Making RazorPage handle only IHtmlContent and clearing out other types.
- Making StringCollectionTextWriter use BufferedHtmlContent so that it can be returned where necessary.
- Updating places which involve Write/Copy to pass in encoders.
- The encoders are currently not being used during write. But when HtmlString is modified to carry encode metadata, the encoder can be used for writing. This is a perf optimization and hence not a part of this change.
- Making TagHelperContent implement IHtmlContent.