Revert "[core] Don't use GL_LINEAR if panning w/o rotation nor pitch"

This reverts commit a70bfd8910.

src/mbgl/map/map.cpp

@@ -409,6 +409,7 @@ void Map::cancelTransitions() {
 
 void Map::setGestureInProgress(bool inProgress) {
     impl->transform.setGestureInProgress(inProgress);
+    impl->onUpdate(Update::Repaint);
 }
 
 bool Map::isGestureInProgress() const {

src/mbgl/map/transform_state.cpp

@@ -175,6 +175,10 @@ float TransformState::getPitch() const {
 
 #pragma mark - State
 
+bool TransformState::isChanging() const {
+    return rotating || scaling || panning || gestureInProgress;
+}
+
 bool TransformState::isRotating() const {
     return rotating;
 }

src/mbgl/map/transform_state.hpp

@@ -60,6 +60,7 @@ public:
     float getPitch() const;
 
     // State
+    bool isChanging() const;
     bool isRotating() const;
     bool isScaling() const;
     bool isPanning() const;