Ignore comments within String constants

This code is too simple.

https://github.com/diffplug/selfie/blob/6c3d0ee489152ff87aff5251b05e75314491ad3c/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/guts/CommentTracker.kt#L51-L54

https://github.com/diffplug/selfie/blob/6c3d0ee489152ff87aff5251b05e75314491ad3c/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/guts/SourceFile.kt#L83-L87

For example:

```java
class Test {
@Test public void example() {
expectSelfie("underTest").toBe("""
This is a string constant
// selfieonce
The comment above is not really a comment.
We effectively have a "forbidden value" that can't be inside inline snapshots.
""")
}
}
```