fix: type error while esModuleInterop is true

[whxaxes]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

当 tsconfig.json 中配置 "esModuleInterop": true 后 tsc 编译的时候会报这个错

491:39 Type 'typeof Application' is not a constructor function type.
    489 |   }
    490 | 
  > 491 |   export class EggApplication extends KoaApplication { // tslint:disable-line
        |                                       ^
    492 |     /**
    493 |      * The current directory of application
    494 |      */

原因是 import KoaApplication 是这么写的

import * as KoaApplication from 'koa';

而 koa 中用的是 export = Application 这种 commonjs 的声明暴露方式，遇到 esModuleInterop 会有问题，所以改成针对这种 export 方式的，又需要用到默认 export 出来的类型的，都用 import XX = require('xxx') 的方式来兼容。

[codecov]

Codecov Report

Merging #3436 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3436      +/-   ##
==========================================
- Coverage   99.78%   99.76%   -0.02%     
==========================================
  Files          32       29       -3     
  Lines         910      844      -66     
==========================================
- Hits          908      842      -66     
  Misses          2        2

Impacted Files	Coverage Δ
lib/egg.js	100% <0%> (ø)	⬆️
...ps/master-worker-started/node_modules/egg/index.js	100% <0%> (ø)	⬆️
lib/core/messenger/index.js
lib/start.js
lib/core/messenger/ipc.js
lib/core/messenger/local.js
lib/core/messenger.js	100% <0%> (ø)

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[atian25]

等单测跑完你就合并吧