"HTML" name for ViewComponents and TagHelpers not generated correctly if class name contains extended letters

[ElJacoTaco]

Class names in C# allow extended letters like ÅÄÖ. When using pascal casing and a new word begins with an extended letter like TestÄa the generated markup is wrong.

Steps to reproduce:

1. Create a ViewComponent with the class name TestÄh.
2. Generated markup to use it should be <vc:test-äa>
3. Generated markup is <vc:testäa>

The actual issue is with the regex here:

razor/src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/HtmlConventions.cs

Line 23 in dde7fe8

"(?<!^)((?<=[a-zA-Z0-9])[A-Z][a-z])|((?<=[a-z])[A-Z])",

Solution:
Change the regex so it supports extended letters just like class names do.

[jjonescz]

Thanks for reporting this issue. However, fixing this would break users that rely on the current behavior (and they wouldn't notice the break until runtime). Given that and the narrow impact of the bug, we likely won't fix it.

[jjonescz]

A non-breaking alternative would be to generate both tag helpers (<vc:test-äa> and <vc:testäa>). See this conversion: #10866 (comment). I'm reopening so this alternative gets triaged.