Export bounds fix

[rpgshooter]

Admin edit: Renamed enums, changed importer script to select slices or regions, and set r16 exports to use _master_height_range instead of normalized per file so all regions/slices are consistent.

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Fixes #821

Adds bounded export functionality to export_image() and layered_to_image() with automatic 16k chunking support.

New ExportMode enum:

• EXPORT_SLICES (default) - Exports full terrain, auto-chunked at 16k boundaries
• EXPORT_REGIONS - Exports each region as a separate file

Modified functions:

• export_image(file_name, map_type, mode) - Added optional mode parameter
• layered_to_image(map_type, bounds) - Added optional Rect2i bounds parameter

Output logging includes:

• Filename
• Size (pixels)
• Position (pixel and world coordinates)

Usage

var data = terrain.get_data()

# Sliced export (default) - auto-chunks if terrain > 16k
data.export_image("res://terrain.exr", Terrain3DRegion.TYPE_HEIGHT)

# Per-region export - one file per region
data.export_image("res://terrain.exr", Terrain3DRegion.TYPE_HEIGHT, Terrain3DData.EXPORT_PER_REGION)

# Direct bounded export
var img = data.layered_to_image(Terrain3DRegion.TYPE_HEIGHT, Rect2i(0, 0, 8192, 8192))

File naming

• Sliced: filename_00_00.exr, filename_01_00.exr, etc.
• Per-region: filename_00_00.exr, filename_00-01.exr (handles negative coords)
• Single chunk/region: no suffix added

Backward compatible

Default parameters maintain existing behavior - no changes required for existing code.

[rpgshooter]

This is a draft and needs to be squashed, there shouldnt be 200+ additions, merge at same time as pr for c# stuff

[rpgshooter]

Once 9c692a7 and 3eb9146, are squashed, should be good to merge, once all checks are good

[TokisanGames]

Great work. Thanks for the patience in reviewing it. I made some tweaks renaming variables that I felt made more sense, a few fixes, adding the option to the importer script, and setting r16 to use _master_height_range instead of being normalized per file as before.