Add Map category with empty geospatial files

[SimonCropp]

Adds a new Map category with empty template files for geospatial formats.

Extension	Size	Contents
.shp	100 bytes	Shapefile header only, Null shape type, zero records
.shx	100 bytes	Matching shapefile index header
.gpkg	5 KB	GeoPackage with the two mandatory core tables and the three required spatial reference rows
.mbtiles	2 KB	metadata and tiles tables, with the two required metadata rows (name, format)
.pmtiles	130 bytes	PMTiles v3 header, empty root directory, {} metadata

API

• Category.Map, appended after Binary so existing enum values do not shift.
• AllFiles.Maps, AllFiles.MapPaths and AllFiles.MapExtensions.
• Map is handled by UseFile and WriteAllTo.

Text extensions

.geojson, .gpx and .kml are added to the known text extensions, so CreateFile/TryCreateFile with useEmptyStringForTextFiles handle them.

Verification

• Build and all tests pass on every target framework.
• The two SQLite based files (.gpkg, .mbtiles) pass PRAGMA integrity_check, and the GeoPackage has the GPKG application id.
• .shp, .shx and .pmtiles are written to their specs but have not been opened in a GIS tool.

Not included

• .kmz stays in Archive; moving it would break AllFiles.Archives[".kmz"].
• Text formats (.kml, .gpx, .geojson) have no template, matching how .svg and .csv are handled; they are covered as text extensions instead.
• .dbf is skipped since it is a general dBASE format rather than a map.