This patch adjusts the implicit conversion rules involving float2 to
match other parts of Blender, like BKE Conversions, Geometry Nodes, and
the Compositor. The new rules also make much more sense to me on their
own.
The GPU_VEC2 is no currently used for GPU materials as far as I can see,
so this should not be a breaking change.
Pull Request: https://projects.blender.org/blender/blender/pulls/148033
a2146839d7