Incorrect "show series cardinality" using inmem when max-series-per-database limit exceeded

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`SHOW SERIES CARDINALITY` shows incorrect count after `max-series-per-database limit exceeded` errors.

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The `inmem` index manages global and per-shard data structures for tracking measurements and series keys. When a `max-series-per-database limit exceeded` condition occurs for a batch write which includes existing and new keys, all keys are rejected by `CreateSeriesListIfNotExists` and the write does not occur, per the following condition:

https://github.com/influxdata/influxdb/blob/26afe32611a36fd61dcf017658ab5ab316f56a5e/tsdb/index/inmem/inmem.go#L262-L266

However, existing series IDs are added to the per-shard roaring bitmap data structure (`SeriesIDSet`) here:
https://github.com/influxdata/influxdb/blob/26afe32611a36fd61dcf017658ab5ab316f56a5e/tsdb/index/inmem/inmem.go#L216

and:

https://github.com/influxdata/influxdb/blob/26afe32611a36fd61dcf017658ab5ab316f56a5e/tsdb/index/inmem/inmem.go#L252

It is now possible that TSM data for these existing keys does not exist in this shard, if the write is the first for these existing keys in this shard. When an older shard drops, series keys are removed from the global inmem data structure iif the associated series id does not exist in any of the *per-shard* `SeriesIDSet` containers.
* this means that the inconsistent per-shard `SeriesIDSet` containers will prevent series IDs from being dropped from the global per:

https://github.com/influxdata/influxdb/blob/26afe32611a36fd61dcf017658ab5ab316f56a5e/tsdb/store.go#L729-L743

This scenario would result in inflated `[database].numSeries` values and the `SHOW SERIES CARDINALITY` commands.

## Secondary Bug

Writes are incorrectly rejected when a batch of writes contains fewer new keys, such that the total series for the database, if the write were to succeed is ≤ `max-series-per-database`.

Specifically, the following logic:

https://github.com/influxdata/influxdb/blob/26afe32611a36fd61dcf017658ab5ab316f56a5e/tsdb/index/inmem/inmem.go#L263

should use `newSeriesN` rather than `len(keys)`:

```go
if max := opt.Config.MaxSeriesPerDatabase; max > 0 && len(i.series)+newSeriesN > max {
```