Replace the SelfContained & _IsPortable property with UseAppHost

[vijayrkn]

@peterhuene @natemcmaster

[peterhuene]

Note that this depends on dotnet/sdk#2282, which hasn't been merged yet.

[vijayrkn]

Note*: I do fallback to $(SelfContained) if $(UseAppHost) is not set. So this change should be backward compatible.

[vijayrkn]

@JunTaoLuo

[peterhuene]

Just wanted to note that the work hasn't been merged in case there's some additional UX feedback that causes the property name or the default behavior to change (we're still discussing it between several different parties).

[vijayrkn]

@peterhuene - Since this (dotnet/sdk#2282) is merged & property name is the same - 'UseAppHost', are we good to merge this PR?

/cc @mlorbetske

[peterhuene]

I think this is good to merge 👍

[vijayrkn]

@natemcmaster @JunTaoLuo - is there any other commits in master that needs to be in 4xx branch?

[vijayrkn]

Closing this in favor of this PR - #356

[natemcmaster]

Not that I'm aware of. It looks like 4xx has everything 3xx has. I don't think anything on master needs backporting (except #355, but that's pending shiproom approval)