Switch to dart-sass from deprecated node-sass (#327)

* Remove node-sass use in extension-webpack-tools and test-apps
* Fix 'Expected identifier' in transition properties.
* Fix additional 'Expected identifier' in transition properties.
* Fix 'Undefined variable' in mixin default values.

Co-authored-by: Gerardas Butkevicius <10091419+GerardasB@users.noreply.github.com>

common/changes/@bentley/extension-webpack-tools/drop-node-sass_2020-12-11-16-19.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@bentley/extension-webpack-tools",
+      "comment": "Switch to 'sass' from the now deprecated 'node-sass' package. Switch from fast-sass-loader to sass-loader due to incompatibility with 'sass' and 'fast-sass-loader'",
+      "type": "none"
+    }
+  ],
+  "packageName": "@bentley/extension-webpack-tools",
+  "email": "31107829+calebmshafer@users.noreply.github.com"
+}

common/changes/@bentley/ui-core/drop-node-sass_2020-12-11-18-07.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@bentley/ui-core",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@bentley/ui-core",
+  "email": "31107829+calebmshafer@users.noreply.github.com"
+}

common/changes/@bentley/ui-ninezone/drop-node-sass_2020-12-11-18-07.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@bentley/ui-ninezone",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@bentley/ui-ninezone",
+  "email": "31107829+calebmshafer@users.noreply.github.com"
+}

common/config/rush/browser-approved-packages.json

@@ -486,10 +486,6 @@
       "name": "faker",
       "allowedCategories": [ "backend", "common", "frontend", "internal" ]
     },
-    {
-      "name": "fast-sass-loader",
-      "allowedCategories": [ "tools" ]
-    },
     {
       "name": "fast-sha256",
       "allowedCategories": [ "tools" ]
@@ -654,10 +650,6 @@
       "name": "nock",
       "allowedCategories": [ "backend", "common", "integration-testing", "internal" ]
     },
-    {
-      "name": "node-sass",
-      "allowedCategories": [ "internal", "tools" ]
-    },
     {
       "name": "nodemon",
       "allowedCategories": [ "tools" ]
@@ -866,6 +858,14 @@
       "name": "rxjs",
       "allowedCategories": [ "frontend" ]
     },
+    {
+      "name": "sass",
+      "allowedCategories": [ "internal", "tools" ]
+    },
+    {
+      "name": "sass-loader",
+      "allowedCategories": [ "tools" ]
+    },
     {
       "name": "save",
       "allowedCategories": [ "internal" ]