fix: use contain_but_size for placeholder-text

Default values in configs become visible

Author: aminya

static/core-ui/text-editor.less

@@ -120,7 +120,7 @@ atom-text-editor {
   }
 
   .placeholder-text {
-    contain: @contain_all;
+    contain: @contain_but_size;
     position: absolute;
     color: @text-color-subtle;
   }