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?**

Comienza con packages/angular_devkit/architect/src/index_spec.ts y reproduce el fallo usando yarn bazel test //packages/angular_devkit/architect:architect_test. Sigue el contexto del builder a través de packages/angular_devkit/architect/src/create-builder.ts, que es donde apunta el stack, y verifica que scheduleBuilder proporcione un target que coincida con su interfaz de TypeScript declarada. Se considera terminado cuando el test enfocado de architect pasa con un target válido.

Escrito por el modelo de indexación a partir del texto del issue.