fix(@ngtools/webpack): fix error with object spread

[hansl]

The loader throws an exception when an object spread is used. This fixes it.

Fixes #4600

[WonderPanda]

When can we expect these changes to available in an NPM update?

[Emnalyeriar]

Is this implemented in RC.1? It doesn't work for me
Example:

    case userActions.ActionTypes.DELETE_USER: {
      return {
        ...initialState
      }
    }

Error:

Type '{ initialState: State; }' is not assignable to type 'State'.
  Object literal may only specify known properties, and 'initialState' does not exist in type 'State'.)

Here is the code running correctly in Typescript playground:
http://www.typescriptlang.org/play/#src=interface%20State%20%7B%0D%0A%20%20%20%20name%3A%20string%0D%0A%7D%3B%0D%0A%0D%0Aconst%20initialState%3A%20State%20%3D%20%7B%0D%0A%20%20%20%20name%3A%20'test'%0D%0A%7D%3B%0D%0A%0D%0Afunction%20reducer()%3A%20State%20%7B%0D%0A%20%20%20%20return%20%7B%0D%0A%20%20%20%20%20%20%20%20...initialState%0D%0A%20%20%20%20%7D%0D%0A%7D%0D%0A%0D%0Aconsole.log(reducer())%3B

[oskarstrasburger]

+1

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