Remove geometries that do not match primary mapping geometry type

[spwoodcock]

Describe the bug

• During project creation the user can upload mixed geometries, or the data extract via raw-data-api is often mixed.
• The user specifies they want to map a particular geom type.
• There is a mismatch here: the user has points to map when the specified they are mapping polygons.

Follow on from #2225

Expected behavior

We need to either:

1. Strip all geoms that do not match the primary mapping geom type. This is easy for custom data extracts. For raw-data-api data extracts, prerequisites are Allow project creators to select specific feature types for OSM data download #2193 and Data extracts from raw-data-api should always be downloaded, update project creation workflow #2175
2. OR allow the mapping of mixed geometry types. But to enable this we need to fix the styling of both geometry types at once in the svelte-maplibre map component of the mapper frontend.

The question is: do we ever need to map mixed geometry types at the same time?
If so, this probably adds significant complication - is the gain worth it?