For custom analyzer position_offset_gap renamed to position_increment_gap

[AlexMihalev]

NEST/Elasticsearch.Net version: 7.4.1

Elasticsearch version: 7.3.0

The position_increment_gap can't be specified in the case of the custom analyzer. Only PositionOffsetGap (see ICustomAnalyzer.PositionOffsetGap) is available but it looks like its deprecated and ignored by Elastic Search (see https://www.elastic.co/guide/en/elasticsearch/reference/7.5/analysis-custom-analyzer.html#)

Seems it has been renamed to position_increment_gap.

[codebrain]

Ported to 7.x and 7.6