Javascript should support property assignments on `exports`, even when aliased

[sandersn]

// @allowJs: true
// @checkJs: true
// @noEmit: true
// @Filename: semver.js
exports = module.exports = C
exports.f = n => n + 1
function C() {
    this.p = 1
}
// @filename: index.js
const C = require("./semver")
var two = C.f(1)
var c = new C

Expected behavior:
In index.js, f should be a member of C.

Actual behavior:
It is not.

Note that if you assign to C, f is visible, but only if the assignment occurs after function C () { ... }. But that's a separate bug.