ReplicaReadMixed in leader-and-follower / closest-replicas / closest-adaptive also tries learner replicas but docs say only leader & follower

[King-Dylan]

File: /release-8.5/follower-read.md When using the replica read options: leader-and-follower closest-replicas closest-adaptive

they are mapped internally to ReplicaReadMixed. However, from the code logic, ReplicaReadMixed will also try learner replicas for reads.

Currently, the official documentation only states that these modes will try leader and follower replicas, and does not mention learner replicas, which can be confusing or misleading to users. refer: https://github.com/tikv/client-go/blob/master/kv/store_vars.go#L65-L66