Asymmetry between supported point format in geo_point and geo_shape field types

[talevy]

Right now geo_point can be defined in multiple formats:

• "POINT(0 0)", WKT
• { "lat": 0, "lon": 0}, lat/lon object
• [0, 0], [lon, lat] array
• "0, 0", (lat, lon) string
• "gbsuv", geohash

Since geo_shape supports point types, it may make sense to also support geo_point formats as field values for this field type.

relates to #47243, where it would be nice to match either geo_point or geo_shape values.

[talevy]

We discussed this in our Analytics/Geo team meeting and concluded that it would be clearer if the parsing of geo fields were consolidated together. This means that all valid geo_point field value formats will also be valid geo_shape field value formats, which will be indexed as Point/MultiPoint geometries. This will enable more flexible support for indexing the same field as both geo_point and geo_shape without modifying the value (even as a multi-field).

As part of this, GeoJSON will also be supported by the geo_point field (see #47815).

[craigtaverner]

The related work in #84599 adds GeoJSON support to geo_point, but does not add the missing point formats to geo_shape, so we re-discussed this in the Analytics/Geo team meeting, and the consensus was that expanding geo_shape format support was not valuable, and in fact expanding support comes with the need to maintain that long term, so it was not desirable. In fact it was even suggested to deprecate the older point formats from geo_point.

However, the work involved in deprecation is high, and there is a definite risk that existing users will be impacted by such a change. The final position is to not fix this issue. Neither by adding old point formats to geo_shape, nor by deprecating the older point formats. Instead we will review all documentation and down-prioritize the older point formats (remove from examples that do not explicitly need them, replacing with WTK or GeoJSON). This issue then becomes a documentation issue. And the older formats are kind-of soft-deprecated. Still supported, but not preferred.