feat: mp-weixin getSystemInfo safeAreaInsets

src/platforms/mp-weixin/runtime/api/protocols.js

 import previewImage from '../../helpers/normalize-preview-image'
+
+function addSafeAreaInsets (result) {
+  if (result.safeArea) {
+    const safeArea = result.safeArea
+    result.safeAreaInsets = {
+      top: safeArea.top,
+      left: safeArea.left,
+      right: result.windowWidth - safeArea.right,
+      bottom: result.windowHeight - safeArea.bottom
+    }
+  }
+}
 export const protocols = {
-  previewImage
+  previewImage,
+  getSystemInfo: {
+    returnValue: addSafeAreaInsets
+  },
+  getSystemInfoSync: {
+    returnValue: addSafeAreaInsets
+  }
 }
-export const todos = [
-  'vibrate'
+export const todos = [
+  'vibrate'
 ]
-export const canIUses = []
+export const canIUses = []