Remove `~/` handling from core Razor.

[Eilon]

Kind of related to #417

Allegedly Razor will resolve paths of all attributes of all HTML attributes, which means that ~'s will be stripped out regardless of whether the HTML (or Tag Helper) attribute represents a path or URL.

We should consider adding some new TagHelper attribute such as [UrlProperty] to indicate that Razor should code-gen path resolution code for the property.

[grahamehorner]

I agree however razor is also striping non-path attributes data-attrib="somedata~" and this may be by design in razor for paths; but what if a tag requires the ~ and it's not a path. I think TagHelpers shouldn't have razor pre-process the tag attributes other than the know HTML attributes that are path related.

[Eilon]

@grahamehorner right, this bug is exactly to stop processing ~ in places where it's not a URL. Only href and src and perhaps some other specific HTML attributes should have URL processing.