get_item_rect_size for plot annotations?

**Is your feature request related to a problem? Please describe.**
I'm trying to distribute a large amount of plot annotations dynamically in such a way that they don't overlap - and for that, I need the pixel sizes of the annotations. However, get_item_rect_size gives me a KeyError: 'rect_size', as the item_state dict is just {'ok': True, 'pos': [0, 0]}.
**Describe the solution you'd like**
Would be great to have get_item_rect_size working for annotations.

**Describe alternatives you've considered**
Is it possible to get the character heights/widths from the font textures directly? I assume those textures are saved somewhere explicitly, but I have no idea how to get them.