Updates to channel init registration ordering:
* Add ability to float filters towards the top of the stack or to sink them towards the bottom. This is a secondary hint to the explicit ordering constraints that we have. To avoid possible ambiguities we enforce that there can never be two tops/two bottoms available to add simultaneously (if this eventuality appears we simply require an explicit ordering between the two filters).
* Add the ability to skip some filters in the V2 stack (so we can start building V3 only filters)
Along the way:
* Add hashability to `UniqueTypeName`
* Remove `UniqueTypeName` copy constructor (this is just the default copy constructor anyway, and its presence started to confuse `clang-tidy`).
* Separate the dependency tracking and logging parts of channel_init.cc. This was necessary for my brain to be able to process how to implement the new ordering constraints. Happily, it also eliminates an O(n**2) loop in initialization!
Closes#36993
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36993 from ctiller:ordering-innit e9d08e7a81
PiperOrigin-RevId: 646144240
Craig Tiller