Improve layer settings performances

[offtherailz]

While implementing #9099, I noticed a performance problem in layer settings. (TOCItemSettings)

This is due basically to the current implementation and some forced rerenders of all the plugin forced to support the thematic layer plugin. These force re-render are due to some changes applied to the core objects only to support Thematic Layer

We need to refactor and cleanup the implementation of the plugin at least to allow to type data without visible performance issues.
Now a change causes 150ms-200ms re-rendering (this is masked basically by making the input boxes update the fields on blur, but we can not workorund this problem anymore).
This have to be fixed if we want to type and change things live, and for handling easely the future changes to this tool, too.

Here a sample of the warning.

Peek.20-04-2023.15-21.mp4