Reconsider `Foo<>` means default instance

From design discussed here https://github.com/microsoft/typespec/issues/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

```ts
model Template {
x: T
}
```
1. `Template<>` would reference the default instance (`Template`)
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 https://github.com/microsoft/typespec/issues/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