cmd/tsconnect: switch to TypeScript

Continues to use esbuild for development mode and building. Also
includes a `yarn lint` script that uses tsc to do full type checking.

Fixes #5138

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

cmd/tsconnect/package.json

@@ -2,9 +2,15 @@
   "name": "@tailscale/ssh",
   "version": "0.0.1",
   "devDependencies": {
+    "@types/golang-wasm-exec": "^1.15.0",
+    "@types/qrcode": "^1.4.2",
     "qrcode": "^1.5.0",
+    "typescript": "^4.7.4",
     "xterm": "^4.18.0"
   },
+  "scripts": {
+    "lint": "tsc --noEmit"
+  },
   "prettier": {
     "semi": false,
     "printWidth": 80