Replace hardcoded brush with support for raster brush masks

brush_soft_mask.png.import

@@ -0,0 +1,14 @@
+[remap]
+
+importer="image"
+type="Image"
+uid="uid://bbdh4btpg08do"
+path="res://.godot/imported/brush_soft_mask.png-211f364dba674d8d697543d1b1246d6a.image"
+
+[deps]
+
+source_file="res://brush_soft_mask.png"
+dest_files=["res://.godot/imported/brush_soft_mask.png-211f364dba674d8d697543d1b1246d6a.image"]
+
+[params]
+

terrain_cursor_emission.png.import

@@ -1,36 +0,0 @@
-[remap]
-
-importer="texture"
-type="CompressedTexture2D"
-uid="uid://dmbae0p1ujwcv"
-path.s3tc="res://.godot/imported/terrain_cursor_emission.png-242c595842e9c0210b5a4ae1147e42e6.s3tc.ctex"
-path.etc2="res://.godot/imported/terrain_cursor_emission.png-242c595842e9c0210b5a4ae1147e42e6.etc2.ctex"
-metadata={
-"imported_formats": ["s3tc", "etc2"],
-"vram_texture": true
-}
-
-[deps]
-
-source_file="res://terrain_cursor_emission.png"
-dest_files=["res://.godot/imported/terrain_cursor_emission.png-242c595842e9c0210b5a4ae1147e42e6.s3tc.ctex", "res://.godot/imported/terrain_cursor_emission.png-242c595842e9c0210b5a4ae1147e42e6.etc2.ctex"]
-
-[params]
-
-compress/mode=2
-compress/lossy_quality=0.7
-compress/hdr_compression=1
-compress/bptc_ldr=0
-compress/normal_map=0
-compress/channel_pack=0
-mipmaps/generate=true
-mipmaps/limit=-1
-roughness/mode=0
-roughness/src_normal=""
-process/fix_alpha_border=true
-process/premult_alpha=true
-process/normal_map_invert_y=false
-process/hdr_as_srgb=false
-process/hdr_clamp_exposure=false
-process/size_limit=0
-detect_3d/compress_to=0