Replace IHostingEnvironment with IWebHostEnvironment

[Tratcher]

This is the second half of dotnet/extensions#966

IHostingEnvironment is replaced by IWebHostEnvironment
IApplicationEnvironment is replaced by Extensions.Hosting.IHostApplicationEnvironment

Due to the size and timing of this PR nits in samples or tests are unlikely to be addressed.

Also, there are quite a few public constructors that were modified. These are primarily invoked by DI and there is little end-user impact. I'm not keeping the old constructors as the old types are not convertible to the new types. Removing the old constructors seems preferable to obsoleting them with an error.

[JunTaoLuo]

When tests pass.

[davidfowl]

I dunno why this was made public in the first place.

[tebeco]

dumb question but why not align interface name ?
IXxxHostEnvironment or IHostYyyEnvironment

when people are going to find IHostApplicationEnvironment it will probably NOT be straightforward to think that you actually have to backspace back to I to re-type Web

that’s a really naive question there are probably tons of better reason than doing
IWebHostEnvironment
IApplicationHostEnvironment

or
IHostWebEnvironnent
IHostApplicationEnvironment

[Tratcher]

The new types are:
IHostEnvironment
IWebHostEnvironment
IHostApplicationLifetime

IHostWebEnvironment doesn't convey any more meaning.

IApplicationHostLifetime sounds slightly better than IHostApplicationLifetime. @davidfowl @glennc?

[Tratcher]

Announcement posted. #7749