Support for `geohash.ST_AS_GEOHASH_POLYFILL`

[damjad]

Is your feature request related to a problem? Please describe.
No function available to convert a polygon to a list of GeoHashes.

Describe the solution you'd like
We have support for converting a polygon to H3 in BigQuery via polyfill. However, our use case needs the same function for GeoHash i.e. geohash.ST_AS_GEOHASH_POLYFILL

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.