Give a better error message with you omit `@get:Rule`

If you forget `@get:Rule`, it should provide a message that says `"Did you forgot @get:Rule? "`

Consider this code:
```kotlin
// forgot to put the @get:Rule
val composeTestRule = createComposeRule()

@Test
fun `test compose stuff`() = with(composeTestRule) {
setContent {
Text("Hi there")
}
}
```

Without `@get:Rule` you get this:
```
java.lang.NullPointerException
at androidx.test.internal.util.Checks.checkNotNull(Checks.java:41)
at androidx.test.ext.junit.rules.ActivityScenarioRule.getScenario(ActivityScenarioRule.java:127)
at androidx.compose.ui.test.junit4.AndroidComposeTestRule_androidKt.getActivityFromTestRule(AndroidComposeTestRule.android.kt:398)
at androidx.compose.ui.test.junit4.AndroidComposeTestRule_androidKt.access$getActivityFromTestRule(AndroidComposeTestRule.android.kt:1)
at androidx.compose.ui.test.junit4.AndroidComposeTestRule_androidKt$createAndroidComposeRule$1.invoke(AndroidComposeTestRule.android.kt:126)
at androidx.compose.ui.test.junit4.AndroidComposeTestRule_androidKt$createAndroidComposeRule$1.invoke(AndroidComposeTestRule.android.kt:126)
at androidx.compose.ui.test.junit4.AndroidComposeTestRule$special$$inlined$AndroidComposeUiTestEnvironment$1.getActivity(ComposeUiTest.android.kt:215)
at androidx.compose.ui.test.AndroidComposeUiTestEnvironment$AndroidComposeUiTestImpl.getActivity(ComposeUiTest.android.kt:449)
at androidx.compose.ui.test.AndroidComposeUiTestEnvironment$AndroidComposeUiTestImpl.setContent(ComposeUiTest.android.kt:538)
at androidx.compose.ui.test.junit4.AndroidComposeTestRule.setContent(AndroidComposeTestRule.android.kt:381)
```

Should add something like this to `ActivityScenarioRule.getScenario` to give a hint:

```kotlin
checkNotNull(scenario) { "scenario was null, did you forgot @get:Rule somewhere?" }
```

Start at ActivityScenarioRule.getScenario(), the entry point named in the issue, and compare its current null handling with the AndroidComposeTestRule stack trace. The work is done when omitting @get:Rule produces a clear message suggesting that annotation instead of the shown NullPointerException.

Written by the indexing model from the issue text.