Refactor building min_zoom calculation (remove scale_rank)

[nvkelso]

In the v1.6 release we made scale_rank and min_zoom more consistent. This issue is making them completely consistent, and then retiring scale_rank (a breaking v2 change).

From the map examples, including the clamping:

scale_rank	min_zoom	color in map
1	13	dark green
2	13.5	¿missing?
3	14	dark blue
4	14.5	light blue
5	15	light green

In the existing building.yaml file:

  - &z13_area_volume
      all:
        any:
          way_area: { min: 5000 }
          volume: { min: 150000 }
        not: { "tags->location": "underground" }
  - &z14_area_volume
      any:
        way_area: { min: 3000 }
        volume: { min: 100000 }
  - &z15_area_volume
      way_area: { min: 20 }
  - &z16_area_volume
      way_area: { min: 10 }

In Bubble Wrap:
problematic at zoom 15

            filter:
                # show footprints for buildings at least one zoom level before they will be extruded
                - { $zoom: 13, scale_rank: [1,2] }
                - { $zoom: 14, scale_rank: [1,2,3] }
                - { $zoom: 15, height: { min: 100 } }
                - { $zoom: 15, area: { min: 500 } }
                - { $zoom: 15, volume: { min: 100000 } }
                - { $zoom: 16, area: { min: 100 } }
                - { $zoom: 16, volume: { min: 50000 } }
                - { $zoom: { min: 17 }, area: true }

In Refill (map):
problematic at zoom 15

        footprints:
            filter:
                any:
                    - { $zoom: [13], scale_rank: [1,2] }
                    - { $zoom: [14], scale_rank: [1,2,3] }
                    - { $zoom: [15], height: { min: 100 } }
                    - { $zoom: [15], area: { min: 500 } }
                    - { $zoom: [15], volume: { min: 100000 } }
                    - { $zoom: [16], area: { min: 100 } }
                    - { $zoom: [16], volume: { min: 50000 } }
                    - { $zoom: { min: 17 }, area: true }

Then the existing scale_rank.csv is:

area::int,height::float,volume::int,landuse_kind,scale_rank
>=100000,*,*,*,1
*,>=250,*,*,1
*,*,>=300000,*,1
>=20000,*,*,*,2
>=5000,*,*,+,2
*,>=150,*,*,2
*,*,>=150000,*,2
>=5000,*,*,*,3
>=3000,*,*,+,3
*,>=100,*,*,3
*,*,>=100000,*,3
>=1000,*,*,*,4
>=500,*,*,+,4
*,*,>=50000,*,4
+,*,*,*,5

Should the building.yaml file change like (I'm fussy on the landuse_kind and 14.5 logic)?

  - &z13_area_volume
      all:
        any:
          way_area: { min: 100000 } # was 5000, larger value from scale_rank CSV
          height: { min: 250 }            # newly added from scale_rank CSV
          volume: { min: 300000 }   # was 150000, larger value from scale_rank CSV
        not: { "tags->location": "underground" }
  - &z14_area_volume
      any:
        way_area: { min: 3000 }     # no change, same as scale_rank CSV (prefer landuse area)
        height: { min: 100 }            # newly added from scale_rank CSV
        volume: { min: 100000 }    # no change, same as scale_rank CSV
       not: { "tags->location": "underground" }  # NEW
# needs corresponding YAML change later on for 14.5 min_zoom assignment
  - &z14d5_area_volume
      any:
        way_area: { min: 500 }     # NEW, same as scale_rank CSV (prefer landuse area)
        height: { min: 100 }          # NEW, same as scale_rank CSV (from z14_area_volume)
        volume: { min: 50000 }   # NEW, same as scale_rank CSV
       not: { "tags->location": "underground" }  # NEW
  - &z15_area_volume
      any:
        way_area: { min: 200 }      # was 20, larger value between scale_rank CSV (100) and map style (500)
        height: { min: 15 }             # NEW, middle ground to remove < 3 story buildings; map style 100
        volume: { min: 10000 }    # NEW, smaller compromise between area * height, map style (100000)
  - &z16_area_volume
      way_area: { min: 10 }          # no change, same as scale_rank CSV, because of backyard sheds
# Implied that features with way_area smaller than 10 are `min_zoom: 17` later in YAML

Originally posted by @nvkelso in https://github.com/tilezen/vector-datasource/pull/1739/files