Fix function-based InflowBC and Outflow postprocessor in PrecursorAction

[smpark7]

Issue

Moltres supports precursor drift with uniform, function-based, or Navier-Stokes coupled velocities.

The current implementation of outlet postprocessors and inlet boundary conditions in PrecursorAction.C with function-based velocities and precursor looping:

1. does not impose an outlet postprocessor for calculating the precursor concentration at the outlet; and
2. imposes the wrong type of inlet boundary condition without any velocity values provided.

These errors lead to:

1. MooseError stating that Reporter name "Outlet_Average_pre1_/value" with type "double" is not declared.; and
2. homogeneous Dirichlet boundary conditions being imposed on the inlet.

How to reproduce

Issue 1:
Replace the lines 26-28 in $MOLTRES/tests/pre/sub.i:

    u_def = ${flow_velocity}
    v_def = 0
    w_def = 0

with:

    constant_velocity_values = false
    u_func = vel_func
    v_func = 0
    w_func = 0

Add the following code block anywhere outside other input sections:

[Functions]
  [./vel_func]
    type = ParsedFunction
    value = ${flow_velocity}
  []
[]

The velocity function imposes the same constant velocity value as the original input file, but the pre_loop.i test fails due to the erroneous function-based velocity boundary conditions imposed by PrecursorAction.C.

Issue 2:
In addition to the code changes to reproduce Issue 1, replace line 401 in PrecursorAction.C:

  if (getParam<bool>("constant_velocity_values"))

with:

  if (getParam<bool>("constant_velocity_values") || !isParamValid("uvel"))

This step fixes Issue 1 but introduces Issue 2.

How to fix

1. Fix the outlet postprocessor implementation logic in PrecursorAction.C as suggested above.
2. Create an inflow boundary condition, similar to PostprocessorInflowBC, for function-based velocities and fix the inlet boundary condition implementation logic in PrecursorAction.C.
3. Create a test for precursor looping with function-based velocities.