Enable the ESLint no-var rule in the src/display/ folder

Previously this rule has been enabled in the `web/` folder, and in select files in the `src/` sub-folders.
Note that a number of the files in the `src/display/` folder were already enforcing the `no-var` rule, and thanks to Prettier the necessary re-writing will be (mostly) handled automatically.

Please find additional details about the ESLint rule at https://eslint.org/docs/rules/no-var

src/display/.eslintrc

@@ -0,0 +1,10 @@
+{
+  "extends": [
+    "../../.eslintrc"
+  ],
+
+  "rules": {
+    // ECMAScript 6
+    "no-var": "error",
+  },
+}

src/display/annotation_layer.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint no-var: error */
 
 import {
   addLinkAttributes,

src/display/api.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint no-var: error */
 
 /**
  * @module pdfjsLib

src/display/display_utils.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint no-var: error */
 
 import {
   assert,

src/display/fetch_stream.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint no-var: error */
 
 import {
   AbortException,

src/display/network.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint no-var: error */
 
 import {
   assert,

src/display/node_utils.js

@@ -13,7 +13,6 @@
  * limitations under the License.
  */
 /* globals __non_webpack_require__ */
-/* eslint no-var: error */
 
 import { BaseCanvasFactory, BaseCMapReaderFactory } from "./display_utils.js";
 import { isNodeJS } from "../shared/is_node.js";

src/display/svg.js

@@ -13,7 +13,6 @@
  * limitations under the License.
  */
 /* globals __non_webpack_require__ */
-/* eslint no-var: error */
 
 import {
   createObjectURL,

src/display/transport_stream.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint no-var: error */
 
 import { assert, createPromiseCapability } from "../shared/util.js";