Stabilize ExtendedSpanBuilder APIs

[jack-berg]

The ExtendedSpanBuilder APIs have been around (in some form) for a while now. They were introduced on 12/7/23 in #6017 and existed in contrib previously. The APIs don't allow you to do anything new, but improve the ergonomics of certain common operations.

In #6497 I left a comment suggesting a change to the APIs I think we should consider prior to stabilization:

The only thing that gives me pause is the SpanCallable, SpanRunnable interfaces. Would be preferable if we didn't introduce our own functional interfaces and could use Callable, Runnable instead. I understand that we loose type safety over the exception type, but could be worthwhile to have an API with types from standard java users are familiar with.

[zeitlinger]

SpanCallable

I get the impression people are not particularly happy about the standard interfaces: https://stackoverflow.com/questions/2248131/handling-exceptions-from-java-executorservice-tasks

[trask]

I'm probably in favor of keeping SpanCallable and SpanRunnable

I think the convenience API because noticeably less convenient if we switch to Callable and Runnable

• startAndRun(Runnable) - we can't bubble up checked exceptions
• startAndRun(Callable) - we have to wrap and rethrow checked exceptions, altering their original type and affecting upstream throws clauses