Move explorer/weights to ui/weights (#1909)

Test plan: Just a move/rename, `yarn test` passes.

src/ui/weights/EdgeTypeConfig.test.js

@@ -9,7 +9,7 @@ import {assemblesEdgeType} from "../../plugins/demo/declaration";
 
 require("../../webutil/testUtil").configureEnzyme();
 
-describe("explorer/weights/EdgeTypeConfig", () => {
+describe("ui/weights/EdgeTypeConfig", () => {
   describe("EdgeTypeConfig", () => {
     function example() {
       const onChange = jest.fn();

src/ui/weights/NodeTypeConfig.test.js

@@ -9,7 +9,7 @@ import {inserterNodeType} from "../../plugins/demo/declaration";
 
 require("../../webutil/testUtil").configureEnzyme();
 
-describe("explorer/weights/NodeTypeConfig", () => {
+describe("ui/weights/NodeTypeConfig", () => {
   describe("NodeTypeConfig", () => {
     function example() {
       const onChange = jest.fn();

src/ui/weights/WeightSlider.test.js

@@ -15,7 +15,7 @@ import {
 
 require("../../webutil/testUtil").configureEnzyme();
 
-describe("explorer/weights/WeightSlider", () => {
+describe("ui/weights/WeightSlider", () => {
   describe("WeightSlider", () => {
     function example(weight: Weight) {
       const onChange = jest.fn();

src/ui/weights/__snapshots__/EdgeTypeConfig.test.js.snap

@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`explorer/weights/EdgeTypeConfig EdgeWeightSlider renders the name along with some Greek characters 1`] = `
+exports[`ui/weights/EdgeTypeConfig EdgeWeightSlider renders the name along with some Greek characters 1`] = `
 <React.Fragment>
   <span
     style={