Introduce an onInit method for when a new viz_type is selected (#4491)

* Introduce an onInit method for when a new viz_type is selected

This allows for clearing certain controls where/when needed. For
instance here, when loading deck_scatter, even if there was a time
granularity picked for the previous viz_type, we want to unselect it.

* making it functional

superset/assets/javascripts/explore/stores/store.js

@@ -81,6 +81,9 @@ export function getControlsState(state, form_data) {
     control.value = formData[k] !== undefined ? formData[k] : control.default;
     controlsState[k] = control;
   });
+  if (viz.onInit) {
+    return viz.onInit(controlsState);
+  }
   return controlsState;
 }
 

superset/assets/javascripts/explore/stores/visTypes.js

@@ -627,6 +627,17 @@ export const visTypes = {
   deck_scatter: {
     label: t('Deck.gl - Scatter plot'),
     requiresTime: true,
+    onInit: controlState => ({
+      ...controlState,
+      time_grain_sqla: {
+        ...controlState.time_grain_sqla,
+        value: null,
+      },
+      granularity: {
+        ...controlState.granularity,
+        value: null,
+      },
+    }),
     controlPanelSections: [
       {
         label: t('Query'),