Dynamic import not correctly in export assignments

[mhegazy]

From #17060 (comment)

This is still an issue when the dynamic import is used when exporting a default object:

export default {
    getInstance: function () {
        return import('./foo2');
    }
}

transpiles to

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.default = {
    getInstance: function () {
        return import('./foo2');
    }
};

whereas naming the export it works:

export let defaultExport = {
    getInstance: function () {
        return import('./foo2');
    }
}

// transpiles to

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.defaultExport = {
    getInstance: function () {
        return Promise.resolve().then(function () { return require('.foo2'); });
    }
};

typescript version: 2.5.3

[mhegazy]

@weswigham can you take a look at this for the TS 2.6 release.