[FLINK-26199] Annotate StatementSet#compilePlan as experimental.

[dmvk]

https://issues.apache.org/jira/browse/FLINK-26199

Fixes the archunit tests for TableAPI.

• We assume that the class annotated as @PublicEvolving needs to have all return types / parameters @PublicEvolving or @public unless explicitly noted otherwise.
• By annotating compilePlan as @Experimental we allow it to return the CompiledPlan which is also annotated as @Experimental

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• db77daf Azure: FAILURE

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Last check on commit db77daf (Wed Feb 16 19:07:56 UTC 2022)

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