Reconsider Foo<> means default instance

[timotheeguerin]

From design discussed here #1163. Creating a new issue as that design discussion had 2 part and 1st is still relevant. This is to rediscuss the 2nd part.

It was decided that given a template

model Template<T  = string> {
  x: T
}

1. Template<> would reference the default instance (Template<string>)
2. Template would reference the uninstantiated template

The thing is right now Template means the default instance already, so this change would not only be a breaking change but I think relatively confusing for spec writers.

https://cadlplayground.z22.web.core.windows.net/?c=bW9kZWwgTTxUID0gc3RyaW5nPiB7CiAgeDogVDsKfQoKYWxpYXMgTURlZmF1bHRJbnN0YW5jZSA9IE07CgrGPkTFMmQxOtEnLng7Cn0%3D

with this issue #1774 also now on the table I think we might want to reconsider the augment decorator scenario which is as far as I can tell the only place where we want to reference the uninstantiated template

[nguerrera]

We seem to be very confused about what Template means:

Notice that the alias is unused but somehow has an impact on things.

I think that I initially said on #1774 that Template was uninstantiated because I did a quick test like above without the alias.