Clone .editorconfig from minetest/master

.editorconfig

@@ -0,0 +1,8 @@
+[*]
+charset = utf-8
+
+[*.{cpp,h,txt,cmake,fsh,vsh}]
+indent_size = 4
+indent_style = tab
+insert_final_newline = true
+trim_trailing_whitespace = true