add initial implementation of LDtk importer with data models and scene builder

assets/PS_Tileset_10_nes.png.import

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+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://c4ssxvikdpnld"
+path="res://.godot/imported/PS_Tileset_10_nes.png-4155769689f4e11687b219cee5a0f90d.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://assets/PS_Tileset_10_nes.png"
+dest_files=["res://.godot/imported/PS_Tileset_10_nes.png-4155769689f4e11687b219cee5a0f90d.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/uastc_level=0
+compress/rdo_quality_loss=0.0
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/channel_remap/red=0
+process/channel_remap/green=1
+process/channel_remap/blue=2
+process/channel_remap/alpha=3
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=1

assets/test.ldtk.import

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+[remap]
+
+importer="ldtk.importer"
+type="PackedScene"
+uid="uid://c4xhtpmir26ah"
+path="res://.godot/imported/test.ldtk-5da58debf60b2ac4adee332e85c3c4bc.tscn"
+
+[deps]
+
+source_file="res://assets/test.ldtk"
+dest_files=["res://.godot/imported/test.ldtk-5da58debf60b2ac4adee332e85c3c4bc.tscn"]
+
+[params]
+
+import_entities=true
+import_tilemaps=true