Architect#scheduleBuilder or context.scheduleBuilder results in incorrect target on context

# 🐞 Bug report

### Command (mark with an `x`)

- [ ] new
- [ ] build
- [ ] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] extract-i18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

### Is this a regression?

Not that I know of

### Description

If a builder is executed via `architect.scheduleBuilder`, that builder is passed a context that doesn't match the declared interface in typescript. The same happens when using `context.scheduleBuilder` if no target is passed via the `scheduleOptions`.

```js
console.log(context.target);
// logs {project: undefined, target: undefined, configuration: undefined}
// but type is {project: string, target: string, configuration?: string} | undefined
```

## 🔬 Minimal Reproduction

Run `yarn bazel test //packages/angular_devkit/architect:architect_test` with the following patch:

```patch
diff --git a/packages/angular_devkit/architect/src/index_spec.ts b/packages/angular_devkit/architect/src/index_spec.ts
index 57d76c5a6..bbd59b3fc 100644
--- a/packages/angular_devkit/architect/src/index_spec.ts
+++ b/packages/angular_devkit/architect/src/index_spec.ts
@@ -36,10 +36,12 @@ describe('architect', () => {

options = {};
called = 0;
- testArchitectHost.addBuilder('package:test', createBuilder(async o => {
+ testArchitectHost.addBuilder('package:test', createBuilder(async (o, ctx) => {
called++;
options = o;

+ expect(ctx.target != null && ctx.target.target == null).toBe(false);
+
return new Promise(resolve => {
setTimeout(() => resolve({ success: true }), 10);
});
```

## 🔥 Exception or Error

Failures:

1) architect runs builders parallel

  Message:

    Expected true to be false.

  Stack:

    Error: Expected true to be false.

        at 

        at packages/angular_devkit/architect/src/index_spec.ts:43:63

        at onInput (packages/angular_devkit/architect/src/create-builder.ts:201:20)

        at SafeSubscriber._next (packages/angular_devkit/architect/src/create-builder.ts:87:17)

## 🌍 Your Environment

Master branch on this repo

**Anything else relevant?**

Bắt đầu với packages/angular_devkit/architect/src/index_spec.ts và tái hiện lỗi bằng yarn bazel test //packages/angular_devkit/architect:architect_test. Theo dõi context của builder qua packages/angular_devkit/architect/src/create-builder.ts, nơi stack trỏ đến, và xác minh rằng scheduleBuilder cung cấp một target khớp với interface TypeScript đã khai báo của nó. Hoàn tất khi test tập trung của architect chạy thành công với một target hợp lệ.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.