Parquet: Allow ParquetRecordBatchReader expose the row plans to read

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

Currently, a ParquetRecordBatchReader would has a plan for read. It's maximum read row count is a fixed-sized number, can we try to expose this?

**Describe the solution you'd like**

Add a `row_count` interface for it, would be like ( the impl is incomplete )

```rust
pub(crate) fn remaining_row_count(&self) -> usize {
match &self.selection {
None => 0,
Some(s) => {
let mut value = 0;
for v in s {
if !v.skip {
value += v.row_count;
}
}
value
}
}
}
```

**Describe alternatives you've considered**

Any row-count like interface is ok

**Additional context**

No here

Locate the ParquetRecordBatchReader implementation and inspect how its current read plan and selection are represented. Determine how a row-count interface should expose the remaining planned rows, then verify that the reader reports the expected count for selected and skipped row groups.

Written by the indexing model from the issue text.