Diagnostics stacktrace

[timotheeguerin]

We should find a way to show the diagnostics happening in template instance at a better location

There is a lot of validation that cannot be represented right now as template constraints and even if we supported most there is probably still some things that are out of control.

model Foo<T> {
  @format("uri")
  foo: T;
          ^ error shows up here saying `int32`is not valid for `@format`
}

op test(): Foo<int32>;

https://cadlplayground.z22.web.core.windows.net/?c=bW9kZWwgRm9vPFQ%2BIHsKICBAZm9ybWF0KCJ1cmkiKQogIGZvbzogVDsKfQoKb3AgdGVzdCgpOsUyaW50MzI%2BOw%3D%3D

Some options could be tracing back to out of the template instance to where the template was instantiated.

[nguerrera]

See also #423 (comment) for example from other compiler.

[markcowl]

@timotheeguerin Add implementation sketch and estimate

[markcowl]

pri: 2