Use stricter C++ type conversions (#4357)

Now, implicit narrowing conversions are only used with wpi::Now(). This
also fixes clang-tidy warnings about C-style casts. For example:
```
== clang-tidy /__w/allwpilib/allwpilib/wpilibNewCommands/src/main/native/include/frc2/command/SwerveControllerCommand.inc ==
/__w/allwpilib/allwpilib/wpilibNewCommands/src/main/native/include/frc2/command/SwerveControllerCommand.inc:95:18: warning: C-style casts are discouraged; use static_cast/const_cast/reinterpret_cast [google-readability-casting]
  auto curTime = units::second_t(m_timer.Get());
                 ^
```
In that case at least, the cast was removed entirely since Get() already
returns a units::second_t.

wpilibcExamples/src/main/cpp/examples/Frisbeebot/cpp/subsystems/ShooterSubsystem.cpp

@@ -11,7 +11,7 @@
 using namespace ShooterConstants;
 
 ShooterSubsystem::ShooterSubsystem()
-    : PIDSubsystem(frc2::PIDController(kP, kI, kD)),
+    : PIDSubsystem{frc2::PIDController{kP, kI, kD}},
       m_shooterMotor(kShooterMotorPort),
       m_feederMotor(kFeederMotorPort),
       m_shooterEncoder(kEncoderPorts[0], kEncoderPorts[1]),
@@ -22,7 +22,7 @@ ShooterSubsystem::ShooterSubsystem()
 }
 
 void ShooterSubsystem::UseOutput(double output, double setpoint) {
-  m_shooterMotor.SetVoltage(units::volt_t(output) +
+  m_shooterMotor.SetVoltage(units::volt_t{output} +
                             m_shooterFeedforward.Calculate(kShooterTargetRPS));
 }