Fix NoSuchMethodError in observatory when setting breakpoint via debugger console

Reproduction without this fix:
Create 2 files, test1.dart and test2.dart:

```
$ cat test1.dart
import "test2.dart";

main() {
  test();
  test();
}

$ cat test2.dart
test() {
  // blank line.
  print("hello");
}
```

Launch with observatory enabled and paused at start, e.g.
`out/ReleaseX64/dart --observe --pause-isolates-on-start test1.dart`

Set a breakpoint on the second (*not* the first!) call to `test()`.
Continue execution.
Now write `break test2.dart:2` into the debugger console and you will be
presented with a stack trace looking something like this:

```
Unexpected exception:

NoSuchMethodError: method not found: 'gi4'
Receiver: Instance of 'minified:hS'
Arguments: []

StackTrace:

main.dart.js 459:3      Object.n
main.dart.js 15752:9    hS.G
main.dart.js 15901:28   hS.gi4
main.dart.js 40703:10   GE.$1
main.dart.js 43127:29   Hz.$0
main.dart.js 43100:9    pN.lG
main.dart.js 43124:12   HA.$1
main.dart.js 43127:29   Hz.$0
main.dart.js 43100:9    pN.lG
main.dart.js 43124:12   HA.$1
===== asynchronous gap ===========================
main.dart.js 14033:115  LH.cG
main.dart.js 13585:17   qm.eB
main.dart.js 13571:3    qm.kC
main.dart.js 13870:3    cQ.aV
main.dart.js 13873:27   cQ.I
main.dart.js 40226:79   P.R
===== asynchronous gap ===========================
[...]
```

This CL fixes the issue by catching the NoSuchMethod
(it will succeed for UnresolvedSourceLocation for instance)
and then using the scriptref and token position on the
abstract class Location to get the actual line.

Change-Id: Id951e2727a5edb8ba52a65959c833dcbf923406c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/98667
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>