chore: upgrade webpack/babel build and improve markmap integration (#1934)

Author: Yukaii

.babelrc

@@ -0,0 +1,19 @@
+module.exports = {
+  presets: [
+    ['@babel/preset-env', {
+      targets: {
+        node: '14'
+      },
+      useBuiltIns: 'usage',
+      corejs: 3,
+      modules: 'auto'
+    }]
+  ],
+  plugins: [
+    ['@babel/plugin-transform-runtime', {
+      corejs: 3
+    }],
+    '@babel/plugin-transform-nullish-coalescing-operator',
+    '@babel/plugin-transform-optional-chaining'
+  ]
+}