[WIP] Configure-time specification of which kernels to instantiate for dispatching

[wrtobin]

• CMake functionality for parsing JSON kernel spec and generating source files from templates.
• Add kernel instantiation template source files
• Test on lassen
• Test on tioga
• Test on quartz

[rrsettgast]

hi @johnbowen42 Sorry. I was supposed to do this a couple of weeks ago. @wrtobin had started the task we discussed, but is pretty overloaded. Perhaps you would be ok picking this up?

Here is an issue with some discussion on the matter:
#1994

[wrtobin]

Just grabbed the template source files and default kernels json, which IIRC I was unhappy with the overall format of and was in the middle of modifying / reducing which is why it wasn't already committed.
The kernel template instantiation source file generation should be bare-bones operable after that commit.

[klevzoff]

@johnbowen42 I've just pushed my changes, the code is now in a state where it will compile, link and run (at least it does for me :) ).

It supports reduced kernel specs for kernels under solidMechanics/kernels and multiphysics/poromechanicsKernels. For some of those under fluidFlow, it generates translation units for instantiations, but does not fully support reduced kernel specs because the dispatch on the caller side is not modified and expects the full set of instantiations to be linked. As we discussed, this maybe worthwhile addressing in a follow up PR.