Possibility to set rotation constraint for pal label candidate generation

[jctull]

For new generation labeling, in order to get field-based rotation to work (or even show fields as available), you must also set x and y fields. Additionally, the rotations are not applied unless you edit the layer and move a label.

The expectation is that you can set a field for rotation whether or not you have x and y position fields for a given layer. Additionally, the rotation should be applied without having to first edit the individual labels.

[mhugent]

The new labeling has two distinct modes:

1. fully automatic mode: pal library determines possible positions and rotations (depending on placement options set)
2. fully data defined mode: one candidate position with fixed position and optionally rotation is forced

What you describe would be a way to go with 1. but to specify a rotation. This is not totally impossible, but requires enhancements in the candidate generation code of the pal library. I'm therefore changing the type of this ticket.