STM: MOOSE-Based Scalar Field Transport Modeling

This new MOOSE module focuses on the transport of scalar fields. It will provide a way to describe the conservation laws of scalars, including the effects of advection (bulk fluid motion), diffusion, and reactivity. It will rely on at least two existing MOOSE modules, the chemical reactions module and thermal hydraulics module (THM), to compute reactivity and advective terms, respectively. The new scalar transport module (STM) will likely also draw on the component syntax of THM to make input files more readable for users. It may also use the electromagnetics module to compute ionic species transport in electromagnetic fields. It will be helpful for any groups that need to calculate scalar transport, such as precursor transport in molten salt reactors and ion and neutral transport in (fusion) plasmas.