Eea-api-layout

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* Change: Add `fields` to fixed layout properties (Metadata Section Block)
[avoinea refs 139536]

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* Feature: Add "Dexterity Fixed Layout" Control Panel to be able to configure fixed layout block properties and read-only block properties
[avoinea]

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* Feature: Apply ExtendedFixedLayoutSync by default on all blocks
[avoinea]

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* Feature: Add support for accordionPanel block and propagate readOnlySettings to sub-blocks
[avoinea]

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* Internal: Add doctests for fixed layout sync multi-adapter IFixedLayoutBlockSerializationSync
[avoinea]

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* Feature: Add "volto.blocks.fixed.layout" behavior with auto-sync support
[avoinea]