This PR adds a regression test for cockroachdb#37056. In doing so, it also confirms
the theory that cockroachdb#37055 is the proper fix for that bug.

Before cockroachdb#37055, the test would get stuck with the following logs repeatedly
firing:
```
I190424 00:15:52.338808 12 storage/client_test.go:1242  SucceedsSoon: expected [21 21 21], got [12 21 21]
I190424 00:15:52.378060 78 vendor/go.etcd.io/etcd/raft/raft.go:1317  [s1,r1/1:/M{in-ax}] 1 [logterm: 6, index: 31] rejected msgApp [logterm: 8, index: 31] from 2
I190424 00:15:52.378248 184 vendor/go.etcd.io/etcd/raft/raft.go:1065  [s2,r1/2:/M{in-ax}] 2 received msgApp rejection(lastindex: 31) from 1 for index 31
I190424 00:15:52.378275 184 vendor/go.etcd.io/etcd/raft/raft.go:1068  [s2,r1/2:/M{in-ax}] 2 decreased progress of 1 to [next = 31, match = 31, state = ProgressStateProbe, waiting = false, pendingSnapshot = 0]
```

After cockroachdb#37055, the test passes.

Release note: None

This commit speeds up the test added in cockroachdb#37058 by parallelizing its
failed writes.

Release note: None

Fixes cockroachdb#37085.

This filtering was assuming that the Raft message's index field
indicated the first index in the MsgApp. It actually indicates the
log index that _precedes_ any of the entries in the MsgApp.

It stole this from TestReplicaRangefeedRetryErrors, so the commit
updates that too.

Release note: None