[dart2js] Measure removal of interceptors

[fishythefish]

One area where we think the powerset domain will prove much more effective than typemasks is in removal of interceptors. We can validate this with an analysis similar to #49310:

• Identify where we're able to replace intercepted calls with non-intercepted ones based on the inferred type of the receiver/target.
• Measure how often we're currently able to perform this replacement.
• Measure how often we would replace the call with just the static type + closed world (no typemasks).
• Measure how often we would replace the call with the static type + closed world + powerset domain (no typemasks).