Update jest to version 26.x

Also updates all jest related dependencies to be compatible with
jest@26.

Earlier versions of jest@26 had severe performance impacts, but that has
been resolved with jest@26.5. [0]

Thanks to this update `jest-environment-jsdom-sixteen` can be replaced
with the upstream `"jest-environment-jsdom` which is also based on
jsdom@16.

[0]: https://github.com/facebook/jest/issues/9457#issuecomment-703525151

package.json

@@ -167,9 +167,9 @@
     "@vue/test-utils": "1.0.0-beta.30",
     "acorn": "^6.3.0",
     "axios-mock-adapter": "^1.15.0",
-    "babel-jest": "^24.1.0",
-    "babel-plugin-dynamic-import-node": "^2.2.0",
-    "babel-plugin-istanbul": "^5.1.0",
+    "babel-jest": "^26.5.2",
+    "babel-plugin-dynamic-import-node": "^2.3.3",
+    "babel-plugin-istanbul": "^6.0.0",
     "chalk": "^2.4.1",
     "commander": "^2.18.0",
     "custom-jquery-matchers": "^2.1.0",
@@ -187,11 +187,11 @@
     "jasmine-core": "^2.9.0",
     "jasmine-diff": "^0.1.3",
     "jasmine-jquery": "^2.1.1",
-    "jest": "^24.1.0",
+    "jest": "^26.5.2",
     "jest-canvas-mock": "^2.1.2",
-    "jest-environment-jsdom-sixteen": "^1.0.0",
-    "jest-junit": "^6.3.0",
-    "jest-util": "^24.0.0",
+    "jest-environment-jsdom": "^26.5.2",
+    "jest-junit": "^12.0.0",
+    "jest-util": "^26.5.2",
     "jsdoc": "^3.5.5",
     "jsdoc-vue": "^1.0.0",
     "karma": "^4.2.0",
@@ -214,7 +214,7 @@
     "stylelint-config-recommended": "^2.2.0",
     "stylelint-scss": "^3.9.2",
     "timezone-mock": "^1.0.8",
-    "vue-jest": "4.0.0-beta.2",
+    "vue-jest": "4.0.0-rc.0",
     "webpack-dev-server": "^3.10.3",
     "xhr-mock": "^2.5.1",
     "yarn-check-webpack-plugin": "^1.2.0",
@@ -225,8 +225,7 @@
   },
   "resolutions": {
     "chokidar": "^3.4.0",
-    "monaco-editor": "0.20.0",
-    "vue-jest/ts-jest": "24.0.0"
+    "monaco-editor": "0.20.0"
   },
   "engines": {
     "node": ">=10.13.0",

spec/frontend/environment.js

@@ -2,7 +2,7 @@
 
 const path = require('path');
 const { ErrorWithStack } = require('jest-util');
-const JSDOMEnvironment = require('jest-environment-jsdom-sixteen');
+const JSDOMEnvironment = require('jest-environment-jsdom');
 const { TEST_HOST } = require('./helpers/test_constants');
 
 const ROOT_PATH = path.resolve(__dirname, '../..');