UnusedAssertionDetector reports false positive when assertion is contained in a local function

This works as expected:
```
@Test 
fun test() {
  val result = "some-string"

  assertThat(result).isEqualTo("some-string")
}
```

This fails with a false positive:
```
@Test 
fun test() {
  fun Assert<String>.assertResult() {
   this.isEqualTo("some-string")
  }

  assertThat("").apply { assertResult() }
}
```