Fixes PrecursorAction with velocity functions, and supports higher order precursor variable initialization

[smpark7]

Fixes #183. Fixes #265.

Description

PrecursorAction allows users to define their velocity values for delayed neutron precursor advection using constants, mathematical functions, or MOOSE variables. However, using velocity functions had limited scope due to bugs described in #183. With this PR, PrecursorAction will fully support modeling precursor flow with velocity functions (in line with existing functionality with constant or coupled velocity values).

This PR also extends support for modeling precursor variables with higher (>0) order discontinuous variables.

Changes

• New PrecursorAction Enum input parameter velocity_type to indicate whether the velocity components are constant, function, or variable
  • Replaces the old constant_velocity_values bool-type parameter
• New SideFunctionWeightedIntegralPostprocessor to calculate precursor outflow at the outlet when using velocity functions
• Edits in PrecursorAction:
  • Check whether users provided the correct type of velocity parameters
  • Initialize precursor advection kernels when using higher order variables
  • Initialize penalty boundary conditions to suppress unphysical numerical oscillations at the inlet near the wall
  • Correctly calculate the outflow precursor concentration when using velocity functions
• New & updated tests for precursor flow modeling with velocity functions and first order variables.
• Update squirrel submodule for PostprocessorVelocityFunctionInflowBC, VelocityFunctionConservativeAdvection, & PostprocessorPenaltyDirichletBC objects required in this bugfix.
• Update MOOSE submodule for general updates
• Fix tests in moltres/problems/2021-cnrs-benchmark/phase-0 which were checking the wrong input file

Impact

• Users can now use velocity functions when modeling precursor flow with core reentry
• Users can now use higher (>0) order precursor variables
• New features/updates from the MOOSE submodule update

[katyhuff]

@smpark7 , what's the status of this one?

[smpark7]

I need to address nathan's comments and rerequest reviews. I'll get on it this week