Clarify subscribe / annouce interaction (moq-wg#525)

Fixes moq-wg#362 moq-wg#267 moq-wg#227 moq-wg#225 moq-wg#79

Invalid SUBSCRIBE_UPDATE is a Protocol Violation (moq-wg#479)

This case seems easily avoidable by a subscriber, so the simplest option
is to close the session.

Fixes moq-wg#455
Fixes moq-wg#467

Rename Track Request Parameters to Subscribe Parameters (moq-wg#451)

Seems like a more obvious name.

Clarify the use of Expires in SUBSCRIBE (moq-wg#406)

And add a new SUBSCRIBE_DONE status code.

Fixes part of moq-wg#390, but it's still unclear how one might refresh a
subscription without interruption.

Land Datagram Preferred (PR moq-wg#342) (moq-wg#344)

Update main to reflect the tx-mode branch after moq-wg#342 was merged.

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