feat(mp-alipay): custom mini.project.json (#3929)

packages/uni-mp-alipay/lib/uni.config.js

 const path = require('path')
-const { parseJson } = require('@dcloudio/uni-cli-shared/lib/json')
+const {
+  parseJson
+} = require('@dcloudio/uni-cli-shared/lib/json')
 
 module.exports = {
   options: {
@@ -17,7 +19,8 @@ module.exports = {
       filter: '.sjs'
     },
     filterTag: 'sjs',
-    subPackages: true
+    subPackages: true,
+    project: 'mini.project.json'
   },
   copyWebpackOptions (platformOptions, vueOptions) {
     const copyOptions = ['mycomponents', 'customize-tab-bar', 'ext.json']

packages/webpack-uni-pages-loader/lib/platforms/mp-alipay.js

+const fs = require('fs')
+const path = require('path')
+
 const {
-  parsePages
+  parsePages,
+  getPlatformProject
 } = require('@dcloudio/uni-cli-shared')
 
 const {
@@ -84,13 +88,21 @@ module.exports = function (pagesJson, manifestJson) {
   if (app.usingComponents) {
     updateAppJsonUsingComponents(app.usingComponents)
   }
+  const projectName = getPlatformProject()
 
-  const project = Object.assign({
-    appid: platformJson.appid
-  })
+  let project = {}
+
+  const projectPath = path.resolve(process.env.UNI_INPUT_DIR, projectName)
+  if (fs.existsSync(projectPath)) {
+    project = require(projectPath)
+  } else {
+    if (platformJson.appid) {
+      project.appid = platformJson.appid
+    }
 
     project.component2 = hasOwn(platformJson, 'component2') ? platformJson.component2 : true
     project.enableAppxNg = hasOwn(platformJson, 'enableAppxNg') ? platformJson.enableAppxNg : true
+  }
 
   return [{
     name: 'app',