Make WindowedValue a public interface

[kennknowles]

The following mostly-automated changes:

• Moved WindowedValue from internal-only util to public values package
• Make WindowedValue an interface with companion class WindowedValues

This is an initial step to #34902 that touches lots of lines and files but is largely automated and has no interesting content. Separating this for ease of review.

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[kennknowles]

R: @ahmedabu98 or @stankiewicz

If you wouldn't mind just scrolling through and convincing yourself I didn't make any nontrivial change.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.44%. Comparing base (60307b4) to head (7904ba3).
Report is 43 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #35159   +/-   ##
=========================================
  Coverage     56.44%   56.44%           
- Complexity     3299     3300    +1     
=========================================
  Files          1185     1185           
  Lines        181910   181915    +5     
  Branches       3409     3409           
=========================================
+ Hits         102682   102689    +7     
+ Misses        75959    75958    -1     
+ Partials       3269     3268    -1     

Flag	Coverage Δ
java	70.61% <ø> (+0.01%)	⬆️

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[stankiewicz]

I've reviewed sdks/java/core/src/main/java/org/apache/beam/sdk/values/WindowedValue.java
and sdks/java/core/src/main/java/org/apache/beam/sdk/values/WindowedValues.java
and skimmed through most of the small changes. .

[kennknowles]

Thanks! Fixing up some reflective access in the SparkRunner before I merge.

[kennknowles]

Dataflow Streaming PipelineTest I looked at job https://console.cloud.google.com/dataflow/jobs/us-central1/2025-06-05_12_06_25-3244368481778048427 and it did not have any error. It did look like it was in a weird state, but had
and also so many other jobs succeeded I don't think it means anything. It takes 7 hours so deflaking is not practical.