Memory usage grows after `editor.getData()` calls

[scofalik]

📝 Provide detailed reproduction steps (if any)

While doing some test on one of our performance samples (init-single with mixed data set), I can see that memory grows around 0.2 MB after every editor.getData() call. Looks like at least some of that is related to tables/slots but working with memory profiler is not easy, so I didn't have enough time to debug it correctly.

I am afraid that it may grow out of hand after, let's say, an hour of working over a big document with autosave working in the background.