improvement(container-runtime): Further simplifications for dirty/saved logic

[markfields]

Description

Some follow-ups to #24646:

• Don't bother calling updateDocumentDirtyState when processing a non-modern-runtime message, since we don't even check for its presence in PendingStateManager
• Get rid of the special treatment of dirty state in replayPendingStates. See commit message on feef9a1fc1014281cf78bd0d663c19e2c4685d57 for details

TODO:

• [ ] write one or two tests

[markfields]

Converting to a draft, not expecting to prioritize this before going on Leave. Will finish the tests and pick it up in August.

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