Breakpoint positions are lossy

Consider the line

```
print(0.toString());
```

both the `print` and `toString` calls can independently have breakpoints.

* DevTools only reports if there is a breakpoint anywhere on the line (lossy reporting of breakpoints set by other precise clients).
* DevTools only allows setting a breakpoint by clicking on the line (lossy setting of breakpoints).

Start by reproducing the example with separate breakpoints on the print and toString calls, then inspect how DevTools reports and sets breakpoints. Done means breakpoint locations are preserved and can be independently reported and set rather than reduced to a line-level result.

Scritto dal modello di indicizzazione a partire dal testo della issue.