Expose path of currently executing view

[DamianEdwards]

The path of the currently executing view would be extremely helpful when tracing information RE view rendering, e.g. from Tag Helpers.

It will likely not work on ViewContext as that flows down to things like partial views. Perhaps a new type is needed, e.g. ViewExecutionContext, on which we make it available. We could investigate making the entire tree of view execution available, e.g. view -> layout -> partial view -> etc.

[yishaigalatzer]

We should consider doing something special for templates (as templates are similar to partial views, but they have a different context), so perhaps some indication of the type of view that the code is executing in (enum? or set of well known strings?).

We had a quick discussion with @pranavkm and we think ViewContext should work.