Table's InsertTableView takes a long time to render

[mlewand]

📝 Provide detailed reproduction steps (if any)

We should improve rendering time of this component.

For instance in case of loading a simple editor with small data sample, it took 60ms, which in turns add up to slow _initToolbar execution. For comparison the entire editor renders in 1.23s so this view alone accounts for almost 5% of the entire initialization time.

✔️ Expected result

Quicker editor UI render 🏃‍♀️

❌ Actual result

InsertTableView takes a lot of time during the initial editor render 🐢 🐢 🐢 🐢 🐢 🐢 🐢 🐢 🐢

📃 Other details

This is a follow-up of #5880.

• Browser: Chrome
• OS: Windows (should be cross system)
• CKEditor version: latest master

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[Reinmar]

Les recalculations 🏃‍♀️

The performance problem here isn't due to recalculations AFAICT, but simply initializing and rendering a lot of UI when not needed.

[mlewand]

The performance problem here isn't due to recalculations

Yea, I copied the expected / actual from #6194. In case of tables, in fact a lot of items are created - something that we could defer.