TileMap Terrains do not show all of the selected options that were selected for that particular terrain

### Tested versions

-Reproducible - 4.2.2.stable
-Reproducible - 4.3. stable

### System information

Windows 10 - Godot 4.3

### Issue description

after setting up a TileSet Tiles with terrains, the TileMap-> Terrains does not show all of the selected options that were selected for that particular terrain. Do they still register? Yes. The issue is minor but annoying. I just want the whole list of what tiles contain that terrain.
Two main issue.
1. The list is missing some tiles.
- A solution to show all the tiles, be it repeated or not, that contain that terrain type on all the Terrain lists.
2. The list shows tiles that do not contain the terrain in question.
- A solution to show only the tiles where the center is the terrain in question. Not the corners or side

### Steps to reproduce

Create Node: TileMapLayer. Set a TileSet. In the TileSet add Elemet and add a couple of Terrains. Under a TileSet, add a tile map and add the terrains for each terrain type. When switching over to TileMap under the Terrains, The tiles show some but not all the tiles that contain the tile that was selected. The engine still counts the tile and still spawn the tile.

### Minimal reproduction project (MRP)

[TileMapLayer-Issue.zip](https://github.com/user-attachments/files/16631205/TileMapLayer-Issue.zip)

Start with the attached TileMapLayer-Issue.zip reproduction project and reproduce the behavior in the TileMap Terrains editor for the configured TileSet terrains. Compare the displayed tiles with the terrain assignments: done means all tiles containing the selected terrain are shown, while tiles with that terrain only on a corner or side are excluded, without changing registration or spawning behavior.

Written by the indexing model from the issue text.