Add an "offset" property to first level symbol (needed for the "Offset point symbols" tool)

[qgib]

Author Name: Harrissou Santanna (@DelazJ)
Original Redmine Issue: 15817

Redmine category:map_tools

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To use the rotate point symbol, one can define a rotation field at the first level of symbol layers and have the tool usable.
To use the offset point symbol, there's no offset option at the first level, meaning that user needs to set the offset field for all symbol layers of the symbol if he wants the global symbol moved.
This is not a consistent behavior between these two tools, imho.

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0