ksys/phys: Add RigidBody::isEntity to make certain checks clearer

The pattern we want to use is:

```
if (isEntity())
  do entity stuff (e.g. get entity motion accessor)
```

or

```
if (!isEntity())
  return;

do entity stuff
```

That's clearer than

```
if (isSensor())
  return;

do entity stuff
```

because the fact that !isSensor() is equivalent to isEntity() is not
always immediately clear.

src/KingSystem/Physics/RigidBody/physRigidBody.cpp

@@ -326,7 +326,7 @@ bool RigidBody::setLinearVelocity(const sead::Vector3f& velocity, float epsilon)
         return false;
     }
 
-    if (!isSensor() && RigidBodyRequestMgr::Config::isLinearVelocityTooHigh(velocity)) {
+    if (isEntity() && RigidBodyRequestMgr::Config::isLinearVelocityTooHigh(velocity)) {
         onInvalidParameter(1);
         return false;
     }
@@ -443,7 +443,7 @@ void RigidBody::applyLinearImpulse(const sead::Vector3f& impulse) {
         return;
     }
 
-    if (!isSensor())
+    if (isEntity())
         getEntityMotionAccessor()->applyLinearImpulse(impulse);
 }
 
@@ -459,7 +459,7 @@ void RigidBody::applyAngularImpulse(const sead::Vector3f& impulse) {
         return;
     }
 
-    if (!isSensor())
+    if (isEntity())
         getEntityMotionAccessor()->applyAngularImpulse(impulse);
 }
 
@@ -480,24 +480,24 @@ void RigidBody::applyPointImpulse(const sead::Vector3f& impulse, const sead::Vec
         return;
     }
 
-    if (!isSensor())
+    if (isEntity())
         getEntityMotionAccessor()->applyPointImpulse(impulse, point);
 }
 
 void RigidBody::setMass(float mass) {
-    if (isSensor())
+    if (!isEntity())
         return;
     getEntityMotionAccessor()->setMass(mass);
 }
 
 float RigidBody::getMass() const {
-    if (isSensor())
+    if (!isEntity())
         return 0.0;
     return getEntityMotionAccessor()->getMass();
 }
 
 float RigidBody::getMassInv() const {
-    if (isSensor())
+    if (!isEntity())
         return 0.0;
     return getEntityMotionAccessor()->getMassInv();
 }

src/KingSystem/Physics/RigidBody/physRigidBody.h

@@ -260,6 +260,7 @@ public:
     float getGravityFactor() const;
 
     bool isSensor() const { return mFlags.isOn(Flag::IsSensor); }
+    bool isEntity() const { return !mFlags.isOn(Flag::IsSensor); }
     ContactLayerType getLayerType() const {
         return isSensor() ? ContactLayerType::Sensor : ContactLayerType::Entity;
     }

src/KingSystem/Physics/RigidBody/physRigidBodyMotionSensor.cpp

@@ -286,7 +286,7 @@ void RigidBodyMotionSensor::setLinkedRigidBody(RigidBody* body) {
     }
 
     if (body) {
-        if (!body->isSensor() && mFlags.isOff(Flag::HasLinkedRigidBodyWithoutFlag10)) {
+        if (body->isEntity() && mFlags.isOff(Flag::HasLinkedRigidBodyWithoutFlag10)) {
             RigidBodyMotionEntity* accessor = body->getEntityMotionAccessorForSensor();
             if (accessor && accessor->registerAccessor(this)) {
                 mLinkedRigidBody = body;