*Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.*

Sometimes you want to compare a breakpoint to a baseline or another breakpoint to determine which UI to show or how to handle something. This adds operators so you can check those things.

```dart
Breakpoint.activeBreakpointOf(context) > Breakpoints.large;
```

*List which issues are fixed by this PR. You must list at least one issue.*