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.

wpilibc/src/main/native/cpp/simulation/AnalogEncoderSim.cpp

@@ -27,6 +27,5 @@ units::turn_t AnalogEncoderSim::GetTurns() {
 }
 
 frc::Rotation2d AnalogEncoderSim::GetPosition() {
-  units::radian_t rads = GetTurns();
-  return frc::Rotation2d{rads};
+  return units::radian_t{GetTurns()};
 }