Add .editorconfig: spaces everywhere but NewUI

Signed-off-by: joce <joce@unity3d.com>

MaterialGraphProject/Assets/.editorconfig

+root = true
+
+[*]
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = true
+insert_final_newline = true

MaterialGraphProject/Assets/NewUI/.editorconfig

+root = true
+
+[*]
+indent_style = tab
+indent_size = 4
+trim_trailing_whitespace = true
+insert_final_newline = true