Oversimplification of polygon inner rings in ST_Simplify

[Algunenano]

Initially reported by Komzpa

I went to far when dropping inner rings of polygons in my optimization of inner rings, you can only drop all inner rings when the outer ring collapse, not when any of them collapse.

Bug example:

Select ST_AsText(ST_Simplify('POLYGON((0 0, 100 0, 100 100, 0 100, 0 0), (20 20, 20 40, 40 40, 40 20, 20 20), (1 1, 1 5, 5 5, 5 1, 1 1))'::geometry, 10));
                               st_astext                                
------------------------------------------------------------------------
 POLYGON((0 0,100 0,100 100,0 100,0 0),(20 20,20 40,40 40,40 20,20 20))

Same polygon but with the smaller inner ring first:

Select ST_AsText(ST_Simplify('POLYGON((0 0, 100 0, 100 100, 0 100, 0 0), (1 1, 1 5, 5 5, 5 1, 1 1), (20 20, 20 40, 40 40, 40 20, 20 20))'::geometry, 10));
               st_astext                
----------------------------------------
 POLYGON((0 0,100 0,100 100,0 100,0 0))
(1 row)

PR: ​https://github.com/postgis/postgis/pull/504 Affected 3.0 and master

[Algunenano]

This seems to also explain an fix #4556

[Raul Marin <git@…>]

In 570fbdb/git:

Fix oversimplification of polygon inner rings

This also adapts a MVT test which is checking whether it crashes with an
input or not. Since the exact output depends on the backend
(GEOS vs wagyu), we just ensure the input passes through the function.

Closes #4568
Closes #4556
Closes ​https://github.com/postgis/postgis/pull/504