Avoid computing tag helper documentation strings in compiler

[DustinCampbell]

Fixes #8538

The Razor compiler spends time formatting documentation strings for various tag helper objects, even though it never uses them. Each string is written directly to JSON when tag helpers are serialized. This affects throughput performance when tag helpers are passed from Microsoft.AspNet.Razor.Remote (running in Roslyn OOP) to VS, or when they are written to or read from the project.razor.json file.

This change provides a mechanism for tag helpers to reference a DocumentationDescriptor rather than a string. This descriptor holds onto an ID that refers to the expected string resource and an object[] of arguments if formatting is required. I've ensured that this is a non-breaking change. The Documentation property still exists and can be set on tag helper builders. However, I've gone ahead and updated the compiler to never set that property and to use documentation descriptors instead. The net result is that excess work can be avoided in the compiler and in serialization.

[333fred]

Generally looking good. I would like to see failing earlier in a few places when there is unexpected input; many of my comments apply to the 3 different locations where documentationdescriptors can appear.

[davidwengier]

Tooling side LGTM

[333fred]

One more comment before I sign off.

[DustinCampbell]

Thanks everyone for great suggestions. Much appreciated!