Temporaries graph to drive argument factorisation

[wence-]

[connorjward]

Closing as there is insufficient information here to work from now that members have left the project.

[wence-]

FWIW, this is the mechanism described in Fabio's thesis.

[connorjward]

Ah that's very helpful thank you! I will port this over to Firedrake then so we don't lose this (and do the same for #3848).