Add hover transitions

Add new classes, update test snaps

app/assets/javascripts/pipelines/components/dag/dag_graph.vue

@@ -25,6 +25,11 @@ export default {
     containerClasses: ['dag-graph-container', 'gl-display-flex', 'gl-flex-direction-column'].join(
       ' ',
     ),
+    hoverFadeClasses: [
+      'gl-cursor-pointer',
+      'gl-transition-duration-slow',
+      'gl-transition-timing-function-ease',
+    ].join(' '),
   },
   gitLabColorRotation: [
     '#e17223',
@@ -230,7 +235,10 @@ export default {
         .attr('id', d => {
           return this.createAndAssignId(d, 'uid', LINK_SELECTOR);
         })
-        .classed(`${LINK_SELECTOR} gl-cursor-pointer`, true);
+        .classed(
+          `${LINK_SELECTOR} gl-transition-property-stroke-opacity ${this.$options.viewOptions.hoverFadeClasses}`,
+          true,
+        );
     },
 
     generateNodes(svg, nodeData) {
@@ -242,7 +250,10 @@ export default {
         .data(nodeData)
         .enter()
         .append('line')
-        .classed(`${NODE_SELECTOR} gl-cursor-pointer`, true)
+        .classed(
+          `${NODE_SELECTOR} gl-transition-property-stroke ${this.$options.viewOptions.hoverFadeClasses}`,
+          true,
+        )
         .attr('id', d => {
           return this.createAndAssignId(d, 'uid', NODE_SELECTOR);
         })

app/assets/stylesheets/utilities.scss

@@ -100,3 +100,11 @@
 .gl-pl-7 {
   padding-left: $gl-spacing-scale-7;
 }
+
+.gl-transition-property-stroke-opacity {
+  transition-property: stroke-opacity;
+}
+
+.gl-transition-property-stroke {
+  transition-property: stroke;
+}