Improve contributing experience (#1838)

- speedup tsc using incremental flag
- add Mocha Explorer VSCode extension support

.config/mocha.test-explorer.json

@@ -0,0 +1,10 @@
+{
+    "extension": ["ts"],
+    "package": "./package.json",
+    "require": "ts-node/register",
+    "slow": 500,
+    "spec": ["src/**/*.test.ts"],
+    "ignore": ["src/test/slow/visual.test.ts"],
+    "timeout": 0,
+    "watch-files": ["src/**/*.ts"]
+}

.vscode/extensions.json

@@ -0,0 +1,6 @@
+{
+    "recommendations": [
+        "hbenl.vscode-test-explorer",
+        "hbenl.vscode-mocha-test-adapter"
+    ]
+}

.vscode/settings.json

@@ -9,5 +9,6 @@
     "prettier.enable": true,
     "prettier.configPath": ".config/.prettierrc.json",
     "prettier.ignorePath": ".config/.prettierignore",
-    "eslint.workingDirectories": [".", "./example"]
+    "eslint.workingDirectories": [".", "./example"],
+    "mochaExplorer.configFile": ".config/mocha.test-explorer.json"
 }