builtins: Implement ST_AsEncodedPolyline function

[mknycha]

This function takes the geometry and precision and returns the encoded polyline ASCII.
Works the same as in PostGIS.
Release note (sql change): Implement geo builtin ST_AsEncodedPolyline

Resolves #48872

[blathers-crl]

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[cockroach-teamcity]

This change is 

[mknycha]

@otan could you please review or assign someone else?

[otan]

yep! please put the issue number in the PR description, so that it automatically tags me.

[otan]

bors r+

[craig]

Build failed (retrying...):

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[craig]

Build succeeded:

• GitHub CI (Cockroach)

[mknycha]

yep! please put the issue number in the PR description, so that it automatically tags me.

Sorry, I forgot. I'll remember next time