Improve editor initialization time (scenarios with empty content)

[Mgsy]

📝 Provide a description of the improvement

There are scenarios in which people initialize an empty editor (no content). With typical setups the performance is acceptable, but we noticed room for visible improvements during our initial research.

Let's dive deeper into this scenario.

TODO:

• [UI initialization performance] Research how the UI is initialized (the flow) and which steps take significant amount of time #12682
• Make existing dropdowns initialize their panel content on first open #12890

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[cmak9149]

The improvement should be for inline editor and multi-root editor