Add Vue linting (#13447)

* Add Vue linting

Turns out the .vue files were not linted at all, so I added that as well
as re-indented the file to 2-space and fixed all reasonable issues that
cam up except one case of a unintended side effect for which I have no
idea how to fix it, so the rule was disabled.

* misc tweaks

* update lockfile

* use overrides to include .vue files

* treat warnings as errors on lint-frontend

* also treat stylelint warnings as errors

* use equal sign syntax

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

package-lock.json

@@ -5195,6 +5195,26 @@
         }
       }
     },
+    "eslint-plugin-vue": {
+      "version": "7.1.0",
+      "resolved": "https://registry.npmjs.org/eslint-plugin-vue/-/eslint-plugin-vue-7.1.0.tgz",
+      "integrity": "sha512-9dW7kj8/d2IkDdgNpvIhJdJ3XzU3x4PThXYMzWt49taktYnGyrTY6/bXCYZ/VtQKU9kXPntPrZ41+8Pw0Nxblg==",
+      "dev": true,
+      "requires": {
+        "eslint-utils": "^2.1.0",
+        "natural-compare": "^1.4.0",
+        "semver": "^7.3.2",
+        "vue-eslint-parser": "^7.1.1"
+      },
+      "dependencies": {
+        "semver": {
+          "version": "7.3.2",
+          "resolved": "https://registry.npmjs.org/semver/-/semver-7.3.2.tgz",
+          "integrity": "sha512-OrOb32TeeambH6UrhtShmF7CRDqhL6/5XpPNp2DuRH6+9QLw/orhp72j87v8Qa1ScDkvrrBNpZcDejAirJmfXQ==",
+          "dev": true
+        }
+      }
+    },
     "eslint-scope": {
       "version": "4.0.3",
       "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-4.0.3.tgz",
@@ -14005,6 +14025,49 @@
         "v-tooltip": "^2.0.0-rc.32"
       }
     },
+    "vue-eslint-parser": {
+      "version": "7.1.1",
+      "resolved": "https://registry.npmjs.org/vue-eslint-parser/-/vue-eslint-parser-7.1.1.tgz",
+      "integrity": "sha512-8FdXi0gieEwh1IprIBafpiJWcApwrU+l2FEj8c1HtHFdNXMd0+2jUSjBVmcQYohf/E72irwAXEXLga6TQcB3FA==",
+      "dev": true,
+      "requires": {
+        "debug": "^4.1.1",
+        "eslint-scope": "^5.0.0",
+        "eslint-visitor-keys": "^1.1.0",
+        "espree": "^6.2.1",
+        "esquery": "^1.0.1",
+        "lodash": "^4.17.15"
+      },
+      "dependencies": {
+        "acorn": {
+          "version": "7.4.1",
+          "resolved": "https://registry.npmjs.org/acorn/-/acorn-7.4.1.tgz",
+          "integrity": "sha512-nQyp0o1/mNdbTO1PO6kHkwSrmgZ0MT/jCCpNiwbUjGoRN4dlBhqJtoQuCnEOKzgTVwg0ZWiCoQy6SxMebQVh8A==",
+          "dev": true
+        },
+        "eslint-scope": {
+          "version": "5.1.1",
+          "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-5.1.1.tgz",
+          "integrity": "sha512-2NxwbF/hZ0KpepYN0cNbo+FN6XoK7GaHlQhgx/hIZl6Va0bF45RQOOwhLIy8lQDbuCiadSLCBnH2CFYquit5bw==",
+          "dev": true,
+          "requires": {
+            "esrecurse": "^4.3.0",
+            "estraverse": "^4.1.1"
+          }
+        },
+        "espree": {
+          "version": "6.2.1",
+          "resolved": "https://registry.npmjs.org/espree/-/espree-6.2.1.tgz",
+          "integrity": "sha512-ysCxRQY3WaXJz9tdbWOwuWr5Y/XrPTGX9Kiz3yoUXwW0VZ4w30HTkQLaGx/+ttFjF8i+ACbArnB4ce68a9m5hw==",
+          "dev": true,
+          "requires": {
+            "acorn": "^7.1.1",
+            "acorn-jsx": "^5.2.0",
+            "eslint-visitor-keys": "^1.1.0"
+          }
+        }
+      }
+    },
     "vue-hot-reload-api": {
       "version": "2.3.4",
       "resolved": "https://registry.npmjs.org/vue-hot-reload-api/-/vue-hot-reload-api-2.3.4.tgz",