Fetches the `GtkCellArea` this this was created by.
This is generally unneeded by layouting widgets; however, it is important for the context implementation itself to fetch information about the area it is being used for.
For instance at `GtkCellAreaContextClass.allocate()` time it’s important to know details about any cell spacing that the `GtkCellArea` is configured with in order to compute a proper allocation.
| this |
a `GtkCellAreaContext` |
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the `GtkCellArea` this context was created by. |