Tag Helpers: Replace customer facing Debug.Assert's with parse errors. #174
Description
There's 1 Debug.Assert that is customer facing (linked below) that we need to replace with a parser error to not confuse the user. There may be more than just one customer facing Debug.Assert that we should address. We will revisit each of these exceptions and implement correct behavior when we have time.
The Debug.Assert that I'm referring to is: https://github.com/aspnet/Razor/blob/TagHelpersFeature/src/Microsoft.AspNet.Razor/Parser/TagHelpers/TagHelperParseTreeRewriter.cs#L32
This will explode when a user has malformed TagHelpers because it's not supported yet but will be fixed once we get #104 in. For now lets create a parser error so we don't spam users with Debug.Asserts just because they didn't right accurate HTML that happen to be tag helpers.