[wpiunits] Java units API rewrite (#6958)

Java generics are too limited to do what we need. This refactors generic code previously in Unit and Measure into unit-specific classes that can have unit-safe math operations (notably, times and divide) that can return values in known units instead of a wildcarded Measure<?>.

Unit-specific measure implementations are automatically generated by ./wpiunits/generate_units.py, which generates generic interfaces and mutable and immutable implementations of those interfaces. These make up the bulk of the diff of this PR (approximately 9300 LOC).

This also adds units for angular and linear velocities, accelerations, and momenta; moment of inertia; and torque.

wpiunits/src/main/java/edu/wpi/first/units/CurrentUnit.java

@@ -0,0 +1,105 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.units;
+
+import edu.wpi.first.units.measure.Current;
+import edu.wpi.first.units.measure.ImmutableCurrent;
+import edu.wpi.first.units.measure.MutCurrent;
+
+/**
+ * Unit of electric current dimension.
+ *
+ * <p>This is the base type for units of current dimension. It is also used to specify the dimension
+ * for {@link Measure}: <code>Measure&lt;CurrentUnit&gt;</code>.
+ *
+ * <p>Actual units (such as {@link Units#Amps} and {@link Units#Milliamps}) can be found in the
+ * {@link Units} class.
+ */
+public final class CurrentUnit extends Unit {
+  CurrentUnit(CurrentUnit baseUnit, double baseUnitEquivalent, String name, String symbol) {
+    super(baseUnit, baseUnitEquivalent, name, symbol);
+  }
+
+  CurrentUnit(
+      CurrentUnit baseUnit,
+      UnaryFunction toBaseConverter,
+      UnaryFunction fromBaseConverter,
+      String name,
+      String symbol) {
+    super(baseUnit, toBaseConverter, fromBaseConverter, name, symbol);
+  }
+
+  @Override
+  public CurrentUnit getBaseUnit() {
+    return (CurrentUnit) super.getBaseUnit();
+  }
+
+  /**
+   * Constructs a unit of power equivalent to this unit of electrical current multiplied by another
+   * unit of voltage. For example, {@code Amps.times(Volts)} will return a unit of power equivalent
+   * to one Watt; {@code Amps.times(Millivolts)} will return a unit of power equivalent to a
+   * milliwatt, and so on.
+   *
+   * @param voltage the voltage unit to multiply by
+   * @param name the name of the resulting unit of power
+   * @param symbol the symbol used to represent the unit of power
+   * @return the power unit
+   */
+  public PowerUnit mult(VoltageUnit voltage, String name, String symbol) {
+    return Units.derive(PowerUnit.combine(voltage, this)).named(name).symbol(symbol).make();
+  }
+
+  @Override
+  public Current of(double magnitude) {
+    return new ImmutableCurrent(magnitude, toBaseUnits(magnitude), this);
+  }
+
+  @Override
+  public Current ofBaseUnits(double baseUnitMagnitude) {
+    return new ImmutableCurrent(fromBaseUnits(baseUnitMagnitude), baseUnitMagnitude, this);
+  }
+
+  @Override
+  public Current zero() {
+    return (Current) super.zero();
+  }
+
+  @Override
+  public Current one() {
+    return (Current) super.one();
+  }
+
+  @Override
+  public MutCurrent mutable(double initialMagnitude) {
+    return new MutCurrent(initialMagnitude, toBaseUnits(initialMagnitude), this);
+  }
+
+  @Override
+  public VelocityUnit<CurrentUnit> per(TimeUnit time) {
+    return VelocityUnit.combine(this, time);
+  }
+
+  /**
+   * Creates a ratio unit between this unit and an arbitrary other unit.
+   *
+   * @param other the other unit
+   * @param <U> the type of the other unit
+   * @return the ratio unit
+   */
+  public <U extends Unit> PerUnit<CurrentUnit, U> per(U other) {
+    return PerUnit.combine(this, other);
+  }
+
+  /**
+   * Converts a measurement value in terms of another current unit to this unit.
+   *
+   * @param magnitude the magnitude of the measurement in terms of the other current unit
+   * @param otherUnit the other current unit
+   * @return the value of the measurement in terms of this unit
+   */
+  public double convertFrom(double magnitude, CurrentUnit otherUnit) {
+    return fromBaseUnits(otherUnit.toBaseUnits(magnitude));
+  }
+}