Support assignments and awaiting them

[thomaslombart]

We need to handle the case where a user stores the result of a find* query in a variable and later on await this variable, for example:

test("an example", async () => {
  // set up
  const myButton = findByText(/submit/i)
  await myButton
})

We need to keep track of the user assignements and check on every one of them if the user effectively uses an await statement.