RFR: 8371066: Remove unused class TextSourceLabel and associated class hierarchy

[Phil Race]

On Fri, 31 Oct 2025 17:17:06 GMT, Daniel Gredler <dgredler at openjdk.org> wrote:

> The class `TextSourceLabel` is unused, as is the associated factory method `TextLabelFactory.createSimple(...)`.
> 
> The abstractions provided by the abstract classes `TextLabel` and `ExtendedTextLabel` only make sense when there are two types of text labels (`TextSourceLabel` and `ExtendedTextSourceLabel`). With the deletion of `TextSourceLabel`, both `TextLabel` and `ExtendedTextLabel` can also be removed.
> 
> The JavaDoc for the abstract methods in `TextLabel` and `ExtendedTextLabel`, which are implemented in `ExtendedTextSourceLabel`, was moved to `ExtendedTextSourceLabel` prior to the deletion of these two classes.
> 
> The few small convenience methods in `TextLabel` and `ExtendedTextLabel` were also moved to `ExtendedTextSourceLabel` prior to the deletion of these two classes.
> 
> I would have liked to give the combined `TextLabel` + `ExtendedTextLabel` + `ExtendedTextSourceLabel` class the name `TextLabel`, but I've used `ExtendedTextSourceLabel` instead because it makes the diff much smaller and maximizes code history traceability.
> 
> See initial mailing list discussion: https://mail.openjdk.org/pipermail/client-libs-dev/2025-September/032302.html

@prsadhuk please review.

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PR Comment: https://git.openjdk.org/jdk/pull/28090#issuecomment-3478133064