Remove declared IOException in LeafReader methods that should not be doing I/O

[iverase]

Some APIs in LeafReader declared throws IOException even though, in Lucene’s own implementations they are actually not doing any I/O and probably should never do I/O. They provide quick access to some already load metadata for quickly decide if the index needs to be searched or not.

It is difficult to tell from a developer point of view which methods are doing I /O and which are not because everything throws IOException. Therefore the proposal here is to remove the declared IOException from methods that should not be doing I/O.

In particular I am thinking in this two methods, there might be more:

public abstract PointValues getPointValues(String field);

public abstract Terms terms(String field);

This is changing a public API so it should be a lucene 11 change only.

[iverase]

Others method that can eliminate the declaration are:

 @Override
  public final long getSumDocFreq(String field) throws IOException {
    final Terms terms = terms(field);
    if (terms == null) {
      return 0;
    }
    return terms.getSumDocFreq();
  }

  @Override
  public final int getDocCount(String field) {
    final Terms terms = terms(field);
    if (terms == null) {
      return 0;
    }
    return terms.getDocCount();
  }

  @Override
 public final long getSumTotalTermFreq(String field) throws IOException {
    final Terms terms = terms(field);
    if (terms == null) {
      return 0;
    }
    return terms.getSumTotalTermFreq();
  }