Add Prettier

This adds Prettier and makes it replace tsfmt. VSCode is set to use
Prettier for formatting TypeScript/TSX files and format on save since
Prettier is very fast and does not cause any noticeable delay.

.vscode/extensions.json

@@ -5,7 +5,7 @@
   "recommendations": [
     "amodio.tsl-problem-matcher",
     "dbaeumer.vscode-eslint",
-    "eternalphane.tsfmt-vscode"
+    "esbenp.prettier-vscode"
   ],
   // List of extensions recommended by VS Code that should not be recommended for users of this workspace.
   "unwantedRecommendations": []

.vscode/settings.json

@@ -36,5 +36,13 @@
   "typescript.preferences.quoteStyle": "single",
   "javascript.preferences.quoteStyle": "single",
   "editor.wordWrapColumn": 100,
-  "jest.rootPath": "./extensions/ql-vscode"
+  "jest.rootPath": "./extensions/ql-vscode",
+  "[typescript]": {
+    "editor.defaultFormatter": "esbenp.prettier-vscode",
+    "editor.formatOnSave": true,
+  },
+  "[typescriptreact]": {
+    "editor.defaultFormatter": "esbenp.prettier-vscode",
+    "editor.formatOnSave": true,
+  },
 }