Improve DevTools editing interface

This commit adds the ability to rename or delete keys in the props/state/hooks/context editor and adds tests to cover this functionality. DevTools will degrade gracefully for older versions of React that do not inject the new reconciler rename* or delete* methods.

Specifically, this commit includes the following changes:
* Adds unit tests (for modern and legacy renderers) to cover overriding props, renaming keys, and deleting keys.
* Refactor backend override methods to reduce redundant Bridge/Agent listeners and methods.
* Inject new (DEV-only) methods from reconciler into DevTools to rename and delete paths.
* Refactor 'inspected element' UI components to improve readability.
* Improve auto-size input to better mimic Chrome's Style editor panel. (See this Code Sandbox for a proof of concept.)

It also contains the following code cleanup:
* Additional unit tests have been added for modifying values as well as renaming or deleting paths.
* Four new DEV-only methods have been added to the reconciler to be injected into the DevTools hook: overrideHookStateDeletePath, overrideHookStateRenamePath, overridePropsDeletePath, and overridePropsRenamePath. (DevTools will degrade gracefully for older renderers without these methods.)
* I also took this as an opportunity to refactor some of the existing code in a few places:
  * Rather than the backend implementing separate methods for editing props, state, hooks, and context– there are now three methods: deletePath, renamePath, and overrideValueAtPath that accept a type argument to differentiate between props, state, context, or hooks.
  * The various UI components for the DevTools frontend have been refactored to remove some unnecessary repetition.

packages/react-devtools-shared/package.json

@@ -11,6 +11,7 @@
     "@reach/menu-button": "^0.1.17",
     "@reach/tooltip": "^0.2.2",
     "clipboard-js": "^0.3.6",
+    "json5": "^2.1.3",
     "local-storage-fallback": "^4.1.1",
     "lodash.throttle": "^4.1.1",
     "memoize-one": "^3.1.1",

packages/react-devtools-shared/src/__tests__/__snapshots__/inspectedElementContext-test.js.snap

@@ -1,34 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`InspectedElementContext display complex values of useDebugValue: DisplayedComplexValue 1`] = `
-{
-  "id": 2,
-  "owners": null,
-  "context": null,
-  "hooks": [
-    {
-      "id": null,
-      "isStateEditable": false,
-      "name": "DebuggableHook",
-      "value": {
-        "foo": 2
-      },
-      "subHooks": [
-        {
-          "id": 0,
-          "isStateEditable": true,
-          "name": "State",
-          "value": 1,
-          "subHooks": []
-        }
-      ]
-    }
-  ],
-  "props": {},
-  "state": null
-}
-`;
-
 exports[`InspectedElementContext should dehydrate complex nested values when requested: 1: Initially inspect element 1`] = `
 {
   "id": 2,
@@ -65,6 +36,35 @@ exports[`InspectedElementContext should dehydrate complex nested values when req
 }
 `;
 
+exports[`InspectedElementContext should display complex values of useDebugValue: DisplayedComplexValue 1`] = `
+{
+  "id": 2,
+  "owners": null,
+  "context": null,
+  "hooks": [
+    {
+      "id": null,
+      "isStateEditable": false,
+      "name": "DebuggableHook",
+      "value": {
+        "foo": 2
+      },
+      "subHooks": [
+        {
+          "id": 0,
+          "isStateEditable": true,
+          "name": "State",
+          "value": 1,
+          "subHooks": []
+        }
+      ]
+    }
+  ],
+  "props": {},
+  "state": null
+}
+`;
+
 exports[`InspectedElementContext should include updates for nested values that were previously hydrated: 1: Initially inspect element 1`] = `
 {
   "id": 2,