Wet coil epsilon-NTU model

[AntoineGautier]

The feature branch was created based on what is described in #2001 (comment).

TODO before merging:

• @kim1077 to include (manually) recent local modifications (posterior to 456406e) and UA nominal computation.
  • Included as Buildings.Fluid.HeatExchangers.WetCoilEffectivenessNTUWithRated. @AntoineGautier to refactor within WetCoilEffectivenessNTU.
• Resolve warning

The initial conditions are not fully specified. Dymola has selected default initial conditions.
Assuming fixed start value for the continuous states: hexWetNTU.dryWetCalcs.fullywet.TWatOutHat(start = 283.15)

[AntoineGautier]

@kim1077 See my comments. The main one is the refactoring that I think is required to get rid of a lot of duplicated code from existing classes, which will make the model maintenance really cumbersome.

[AntoineGautier]

@kim1077 I refactored to conditionally include UA_nominal computation. Please see the couple comments I have on the newly added classes.

[AntoineGautier]

@mwetter This was needed to plot the dry fraction hexWetNTU.dryWetCalcs.dryFra and illustrate that the validation case covers all the conditions from fully dry to fully wet (and originally to compare with the dry fraction computed by WetCoilCounterFlow but I see you removed that addition as it triggered an event).
Even if it is not used for validation any more, I think plotting hexWetNTU.dryWetCalcs.dryFra still makes sense to illustrate what the validation case covers.

[mwetter]

@AntoineGautier : Please see #2417

[AntoineGautier]

TODO before merging: investigate the issue in Buildings.Fluid.HeatExchangers.Validation.WetCoilEffectivenessNTUHeating where Dymola computes hexWetNTU_TX.Q1_flow equal to 0 due to hexWetNTU_TX.dryWetCalcs.fullyDry.eps being equal to 0.
This is due to the following code snippet in Buildings.Fluid.HeatExchangers.WetCoilEffectivenessNTU.

  Modelica.Blocks.Sources.RealExpression cp_a2Exp(
    final y = if allowFlowReversal2
    then 
      fra_a2 * Medium2.specificHeatCapacityCp(state_a2_inflow)
      + fra_b2 * Medium2.specificHeatCapacityCp(state_b2_inflow)
    else 
      Medium2.specificHeatCapacityCp(state_a2_inflow))

Setting allowFlowReversal2=false solves the issue.
OCT computes hexWetNTU_TX.Q1_flow properly whatever the setting of allowFlowReversal2.

[AntoineGautier]

This is ready to merge when all tests pass.
(I tracked the workaround for Dymola's bug on the issue page, see #622 (comment)).