Change uses of "Hair" in Cycles UI in the property editor and the
"Hair Info" node to use the "Curves" name to reflect the design
described in T95355, where hair is a use case of a more general
curves data type.

While these settings still affect the particle hair system, the idea
is that if we have to choose one naming scheme to align with, we
should choose the option that aligns with future plans and
current development efforts, especially since the particle
system is considered a legacy feature.

A few notes:

• "Principled Hair BSDF" is not affected since it's meant for hair.
• Python API property identifiers are not affected.