Replacing update on the whole table with an update only on changed rows.
The goal is to update more quickly by just updating the changing content.
The update now focus on osm_id of changed rows, it use index. Add a where clause tags != update_tags(tags, geometry) to ensure only update when changed.
It requires one more trigger and a table to store changed osm_id.
The UPDATE is keep in a function to be reusable for initial setup and trigger update.
It is a based on the already merged https://github.com/openmaptiles/openmaptiles/pull/944
It is a separated PR as less obvious than previous. It replaces the reset of the `rank` field to NULL by missing value resulting of `LEFT JOIN`. It avoid triggering a new update on the table by reset the value then re-seting it to initial or new value.
It addresses #814.
Thanks @frodrigo
82616eaac0