[#28187][Prism] Relax or fix issues in Prism to allow Python pipelines to execute.

[lostluck]

Small grab bag of Prism fixes to make progress with #31583 and #28187. This follows up from #31644 which was about unblocking WordCount.

• Add a debug coder print function to better see structure of coders, for debugging prism coder issues. Intended for targetted usage and may not be a permanent fixture.
• Re-write PCollections that are used as Flatten inputs to use the Flatten's output coder as their coder. Python has a habit of re-deriving coders, so we need to ensure that encoded bytes can be decoded on the other side. Prism doesn't unzip/sink flattens yet, which may make this unnecessary in the future.
• Remove a noisy log about composite URNs. It is no longer useful, especially with Python at this stage.
• recover from panics when building stages and their descriptors, so a prism instance doesn't crash during execution of a sequence of tests. This produces more meaningful test output to users as well, though most failures at this stage represent prism bugs.
• Relaxing OutputTime and Always Trigger in the pre-filter allows more tests to run. Some are failing due to these features not being correctly implemented at this stage, so this is acceptable for now to allow Python usage to advance.
• The Python SDK was very noisy when the GRPC server was hard stopped, vs Gracefully stopped. This removes the noise, but keeps the hard stop after 5 seconds just in case an SDK is taking too long to shut down after the control RPC is closed.

These are tested via the Python SDK validates runner tests at the present time.

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[lostluck]

cc: @damondouglas As an FYI This will probably shift a few of the Java tests as well. I'll be doing an audit of prism issues/PRs and get a targetted list of features to implement (and bugs to fix) for us to burn down the next few months.

[jrmccluskey]

LGTM