- Refactored `WriteAttributeTo` to allow re-use of some of the core attribute writing logic. The refactoring was based on removing the `Begin`/`EndContext` for instrumentation bits which isn't valid in a `TagHelper` attribute scenario.
- Added unit tests to validate attributes are properly added to `TagHelperExecutionContext`.
- Added functional test to validate everything is output as expected with dynamic attributes (encoded and non-encoded).
aspnet/Razor#247
