[#31438] Trigger Precusor work for Prism.

[lostluck]

Mostly locking in some fixes and work to avoid making Triggers impossible to review.
This PR has 3 components.

• Adds the bulk of the Trigger State Machine to be used in a different PR.
  • Excludes handling Processing Time, and Merging Windows at this time.
  • https://s.apache.org/beam-triggers for general handling.
  • Checked understanding against the Java TriggerStateMachine code which supports execution for Java runners.
  • Compressed the logic into less abstract form, and simplified shouldFire and Fire handling into a single isReady tree.
  • While it's building on Prism's state handling, it is not getting serialized and deserialized all the time, saving some memory and processing.
• Fixes a bug WRT state and timer execution: Bundles can't mix timers and data, since there is no ordering guarantee on their processing. Timers or data can be processed first. This is a problem if the other group has later data, avoiding the correctness issue.
  • Fixed by never mixing Data and Timers in the same bundle.
• Works around a legacy bug in Java's TestStream encodings where a value will be encoded with the deprecated "Outer" context, which leads to dropping length prefixes in the String encoder.
  • This mostly allows additional ValidatesRunner tests to pass and execute, critical for Trigger testing.

Part of #31438.

Actual use of the StateMachine will occur in a subsequent PR. Keeping the commented out debug prints for the time being.

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[lostluck]

R: @kennknowles @damccorm @jrmccluskey
cc: @damondouglas

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