Names of FEInterfaceValues functions

[bangerth]

Related to #8884. @jppelteret: FYI

#12411 renamed FEInterfaceValues::jump() into FEInterfaceValues::jump_in_shape_values() and similarly for related functions. But I find these names awkward since they have a plural values when they really only return a single value: the jump in the value of a single shape function. We also only have FEValues::shape_value() and FEValues::shape_gradient(), for example.

We should rename these functions a second time, I believe, and remove the plural.

[tjhei]

One can argue that it is a singular jump between two shape functions and as such accurate.

What do you propose for FEValuesViews::Scalar::average_of_values?

[bangerth]

Ah, I see. One could read it that way. jump_in_values() still sounds plural-y to me because I would write that as "the jump in the value of the function at a point x" -- the function does not have multiple values at a point. But I agree that one could interpret it the way you say.

What do others think?

[tjhei]

What do others think?

We could always go back to jump, which is what I prefer. ;-)

[jppelteret]

One can argue that it is a singular jump between two shape functions and as such accurate.

This was how I understood it as well, and why I chose that naming scheme.