[javac] Add compiler check for integer division in floating-point contexts

[SamCarlberg]

Useful for catching bad behavior when doing math or configuring ratios with integers. Errors can be turned off with @SuppressWarnings("IntegerDivision")

double kV = 12 / 6000; // error: integer division in a floating-point context
double kV = 12. / 6000; // OK
double kV = 12 / 6000.; // OK

int kV = 12 / 6000; // OK, but evaluates to 0

double ratio = 42 / 12; // error: integer division in a floating-point context

@SuppressWarnings("IntegerDivision")
double ratio = 42 / 12; // OK, evaluates to 2

Execution failed for task ':developerRobot:compileJava'.
> Compilation failed; see the compiler output below.
  /Users/sam/code/wpilib/allwpilib/developerRobot/src/main/java/wpilib/robot/Robot.java:10: error: integer division in a floating-point context
    double kV = 12 / 6000;
                   ^
  1 error

Also adds the compiler plugin as a dependency to the developerRobot project for dev testing

[Daniel1464]

At least for this PR, i think that the annotation for disabling this check shouldn't be an @SuppressWarnings annotation since that's used to only disable warnings, whereas this integer division check isn't a warning, but an error that prevents the code from compiling. Ideally, it would be a custom annotation, like @EnableIntegerDivision.

Aside from that, though, I'm not sure how I feel about this idea either. It's definitely a really really helpful feature to have, but I'm afraid of getting students into the mindset that every non-FRC java code they write will also check for integer division this way.