[styles] Better representation of island names according to their size

[patepelo]

Currently all islands are represented at the same zoom level. See the island of Corsica as an example.

Describe the ideal solution
Represent major size islands according to their bbox like it's currently done for water bodies. Find a balance between islands, towns and administrative borders.

Additional context
Example of Corsica

CC: @pastk @biodranik

[patepelo]

cc: @organicmaps/styles

[pastk]

E.g. for waterbodies we have in styles

area|z10-13[natural=water][!tunnel][bbox_area>=4000000],
{font-size: 9;}
area|z10-13[natural=water][!tunnel][bbox_area<4000000],
{text: none;}

We can try use the same approach for islands.

But its unlikely to work out of the box, because atm islands labels are point POIs, i.e. the actual polygon is not stored in the map data.
Maybe if we add a [bbox_area] condition to styles then the generator will automatically make it an areal geometry feature (IDK).
But then it'd mean quite a lot of data will be stored just to be able to calculate an approx area at run-time.

A much more efficient approach would be to calc area sizes at the generation stage and derive several feature types like place-island-small/medium/big.

(so its another case when this "dynamic bbox_area" approach is suboptimal, see #6331)