Cannot resolve TagHelperDesignTimeDescriptors in CoreCLR

[NTaylorMullen]

The impact of this bug is not having <summary> IntelliSense in the Razor editor.

Problem: RazorTooling currently only compiles for CoreCLR/netstandard and Razor ifdefs the design time descriptor code to only run in net45 (how it used to run).

We need to find a way to locate XML locations for assemblies in CoreCLR to make this possible.

[NTaylorMullen]

/cc @danroth27 / @Eilon i'm working on this now feel free to decorate with whatever labels you feel necessary. Taskbughancement is my all encompassing suggestion.

[Eilon]

Sorry, didn't feel like creating a new taskbughancement label 😄

[ToddGrun]

Taylor, will this also fix the missing OutputElementHint info?

[NTaylorMullen]

Yes this will also fix that since it exists on the design time descriptor.