geo/geomfn: implement ST_ClosestPoint({geometry,geometry})

[otan]

Implement ST_ClosestPoint on arguments {geometry,geometry}, which should adopt PostGIS behaviour.

Observers: Please react to this issue if you need this functionality.

For Geometry builtins, please do the following:

• Ideally add a relevant helper function in pkg/geo/geomfn (parse and output related functions can go in pkg/geo). Add exhaustive unit tests here - you can run through example test cases and make sure that PostGIS and CRDB return the same result within a degree of accuracy (1cm for geography).
  • When using GEOS, you can reference the C API for which functions are available. Unfortunately, Windows is not currently supported when using GEOS.
• Create a new builtin that references this function in pkg/sql/sem/builtins/geo_builtins.go. Note that we currently do not support optional arguments, so we define functions that have optional arguments once without the optional argument (using the default value in the optional position), and once with the optional argument.
• Modify the tests in pkg/sql/logictest/testdata/logic_test/geospatial to call this functionality at least once. You can call make testbaselogic FILES='geospatial' TESTFLAGS='-rewrite' to regenerate the output. Tests here should just ensure the builtin is linked end to end (your exhaustive unit tests go the above mentioned packages!).
• Ensure the documentation is regenerated by calling make buildshort. You can also play with it by calling ./cockroach demo --empty afterwards.
• Submit your PR - make sure to follow the guidelines from creating your first PR.

You can follow #48552 for an example PR.

The following additional guidance has been issued on implementing this function:

Re-use the geo/geodist functionality to find closest point

_{🤖 This issue was synced with a spreadsheet by gsheets-to-github-issues by otan on 2023-09-03T23:16:38Z. Changes to titles, body and labels may be overwritten.}

[ArjunM98]

Hi, I'd like to take this on!

I did have a quick question about the implementation of this feature. I noticed you mentioned as guidance that we should re-use the geo/geodist functionality to find the closest point. However, I found in the C API that the function GEOSNearestPoints_r accomplishes the same thing we are looking for. I was wondering if we could reuse this functionality, or if you preferred that it be implemented using the geo/geodist functionality.

[otan]

ah, feel free to use GEOS as long as it gives the same results as PostGIS :)