Correct consistent hashing exchange binding deletion when there are duplicate bindings

[FalconerTC]

Proposed Changes

The x-consistent-hash plugin has unexpected behavior when multiple bindings are established to the same queue (see #3386). This causes the hash ring to enter an invalid state, where messages can not be consistently routed anywhere. When entering this state, the only resolution is to delete and recreate the exchange. To replicate:

1. Create an x-consistent-hash exchange
2. Create a binding to a queue Q1
3. Create a second binding of different weight to queue Q1
4. Delete either binding, or delete Q1

This PR hopes to resolve the Bucket 0 not found errors that occur when the hash ring enters an invalid state. When removing a binding, it adjusts queues based on the buckets being removed rather than the weight specified, which differ only with duplicate bindings.

This is possibly also related to #3001

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Further Comments

I'm not familiar with the project, nor with erlang, so open to any an all suggestions.

This does not fix the greater issue brought up in #3386, where nodes coming up and down result in multiple entries in the hash ring. Longer term, it may be better to disallow adding multiple bindings to a single queue. Given this issue with binding deletion, that feature has probably not been in use much.

[michaelklishin]

This exchange was never meant to be used with duplicate bindings, this is why it has routing key weights.

Handing duplicates is nice but there is a reason why this has gone largely unreported for years: this is not how this plugin is supposed to be used.

[michaelklishin]

Thank you.

[michaelklishin]

Backported to v3.9.x manually (for 3.9.9).

[michaelklishin]

Backported to v3.8.x manually.