Optimize Z9 rendering

[Phyks]

Z9 was quite anomaly in terms of rendering time. It was taking much longer than Z8 and Z10 during pre-computation.

Dominant layer was landuse_gen0. It was using subpixel rendering for landuse, which is useful at very low zoom but seems to be safely discardable at Z9.

Also add checking of way geometries against bboxes to ensure correct usage of geospatial indexes in db.

See as well
gravitystorm/openstreetmap-carto#2874 and gravitystorm/openstreetmap-carto#3458 (comment).

See #644.

Screenshots

Before change

After change

SQL timings

Before change

+-----------+----------------+-----------------------+-----------------+---------------------------+---------+
| Time (ms) | #lines fetched |         Layer         | #fields fetched | Size (text format, in kB) | #points |
+-----------+----------------+-----------------------+-----------------+---------------------------+---------+
|   155739  |     87807      |      landuse_gen0     |        6        |           93472           | 2724436 |
|   72884   |      241       |    protected-areas    |        7        |           21552           |  672438 |
|   21497   |      2886      |    landuse-overlay    |        6        |           75216           | 2337983 |
|   20718   |       64       |    military-overlay   |        6        |            386            |  11941  |
|   14091   |      856       |       water_gen0      |        5        |           19231           |  598569 |
|   13813   |     226936     |       roads_med       |        5        |           31984           |  715500 |
|   10909   |     23439      | bicycle_routes_labels |        9        |           110236          | 3383817 |
|    4262   |     29195      |      waterway_low     |        4        |           10035           |  280558 |
|    4198   |      659       |     admin-low-zoom    |        4        |           22069           |  688972 |
|    3338   |       23       |      state-names      |        6        |           32326           | 1008810 |
|    3125   |       9        |     country-names     |        5        |           20773           |  648968 |
|    1170   |     11270      |  bicycle_routes_gen2  |        6        |            1641           |  35559  |
|    264    |      1470      |   placenames-medium   |        7        |            109            |   1470  |
|     86    |      400       |      ferry-routes     |        4        |            168            |   4846  |
|     33    |       4        |     capital-names     |        6        |             0             |    4    |
+-----------+----------------+-----------------------+-----------------+---------------------------+---------+

After change

+-----------+----------------+-----------------------+-----------------+---------------------------+---------+
| Time (ms) | #lines fetched |         Layer         | #fields fetched | Size (text format, in kB) | #points |
+-----------+----------------+-----------------------+-----------------+---------------------------+---------+
|   22350   |      9067      |      landuse_gen1     |        6        |           203399          | 6321176 |
|   14217   |      856       |       water_gen0      |        5        |           19231           |  598569 |
|   13356   |     226936     |       roads_med       |        5        |           31984           |  715500 |
|   11347   |     23479      | bicycle_routes_labels |        9        |           110715          | 3398663 |
|    8064   |      2886      |    landuse-overlay    |        6        |           75216           | 2337983 |
|    4483   |     29195      |      waterway_low     |        4        |           10035           |  280558 |
|    4434   |      659       |     admin-low-zoom    |        4        |           22069           |  688972 |
|    3300   |       23       |      state-names      |        6        |           32326           | 1008810 |
|    2087   |       9        |     country-names     |        5        |           20773           |  648968 |
|    2034   |      241       |    protected-areas    |        7        |           21552           |  672438 |
|    1341   |     11270      |  bicycle_routes_gen2  |        6        |            1641           |  35559  |
|    428    |       64       |    military-overlay   |        6        |            386            |  11941  |
|    262    |      1470      |   placenames-medium   |        7        |            109            |   1470  |
|     29    |      400       |      ferry-routes     |        4        |            168            |   4846  |
|     16    |       4        |     capital-names     |        6        |             0             |    4    |
+-----------+----------------+-----------------------+-----------------+---------------------------+---------+