Account for changes in eslint-plugin-import version 2.23.0

The simplest solution, as far as I can tell, to "fix" the new errors reported by the `no-unresolved` rules was to extend the existing whitelisting to cover the new cases. Given that the affected `imports` are only relevant in `gulp server`-mode, this should thus be completely fine.

Please find additional information at:
 - https://github.com/benmosher/eslint-plugin-import/releases/tag/v2.23.0
 - https://github.com/benmosher/eslint-plugin-import/blob/v2.23.0/CHANGELOG.md#2230---2021-05-13

Author: Snuffleupagus

external/builder/test-fixtures.js

@@ -1,6 +1,6 @@
 "use strict";
 
-const builder = require("./builder");
+const builder = require("./builder.js");
 const fs = require("fs");
 const path = require("path");
 

src/.eslintrc

@@ -0,0 +1,12 @@
+{
+  "extends": [
+    "../.eslintrc"
+  ],
+
+  "rules": {
+    // Plugins
+    "import/no-unresolved": ["error", {
+      "ignore": ["pdfjs"]
+    }],
+  },
+}

web/.eslintrc

@@ -5,6 +5,8 @@
 
   "rules": {
     // Plugins
-    "import/no-unresolved": ["error", { "ignore": ["pdfjs-lib"]}],
+    "import/no-unresolved": ["error", {
+      "ignore": ["pdfjs", pdfjs-lib", "pdfjs-web"]
+    }],
   },
 }