- For older version of Razor the HTML comments will be complained about by TahHelperRewriter
- RazorParserFeatureFlags tests now ensure that AllowHtmlCommentsInTagHelpers is true in 2.1 version and false in older versions
- Added extra test for IsHtmlCommentAhead to make sure Razor code transition is allowed in comment tag
- Moved the unallowed html comment ending to a static array.
- Restructured RazorLanguageVersion to be a sealed concrete type to enable things like `RazorLanguageVersion.Latest`; it also allows us to make broader changes in the future. Also, in the future if we want to add support for overriding operators to enable greater than comparisons we can as well.
- Removed version validity checks because we restrict who can construct a `RazorLanguageVersion` now. This way we don't have to check for valid versions all throughout our code.
- Added a simple `ProjectExtensibilityConfiguration` => `RazorLanguageVersion` method in the `DefaultProjectExtensibilityConfigurationFactory` to temporarily enable letting the system operate on the `RazorLanguageVersion`. Eventually that entire class will change.
#1961