[C++][Compute][Python] Rename "project" kernel to "make_struct"

The "project" compute Function is necessary for ARROW-11174. However it is not intended for direct use outside an Expression (where the correspondence to projection is not immediately obvious) so it may be preferable to do one/more of:

• rename the function to "wrap_struct" or similar so it does make sense outside Expressions
• ensure the function is not exposed to python/R bindings except through Expressions
• remove the function from the default registry