feat: Support for an attribute-based feature toggling TagHelper

I think this would be extremely straightforward to implement and make for a tidier, less disruptive use of the tag helper.

<ul>
  <!-- Suggestion -->
  <li feat-name="" feat-requirement="" feat-negate="">MenuItem</li>

  <!-- Current -->
  <feature name="" requirement="" negate="">
    <li>MenuItem</li>
  </feature>
</ul>

Required changes:

• Copy FeatureTagHelper into FeatTagHelper (or FeatureAttributeTagHelper)
• Annotate with [HtmlTargetElement(Attributes = nameof(FeatName))]
• Prefix property names with Feat
• Remove output.TagName = null; so the existing HTML element stays in place
• Remove the feat- attributes off the rendered element
• Potentially abstract out an abstract base class to share code between attributes
  • output.TagName = null; can be run if output.TagName == "feature"

It's really quite similar to the ConditionTagHelper in the docs here.

I'm happy to implement this as a PR if it will be accepted. I'll probably be creating one in our repo in the short term.

Start by locating the existing FeatureTagHelper and compare its behavior with the ConditionTagHelper pattern linked in the issue. Implement the attribute-based variant or shared abstraction as appropriate, preserving the original HTML element and removing feature attributes from rendered output; verify both existing and new tag-helper behavior with the repository's tests.