Peng-Robinson EoS: added setState_DP

[TJP-Karpowski]

Changes proposed in this pull request

The Peng-Robinson EoS does not implement a DP update, which is added by this merge request.
The setState_DP function was extended with a Tguess value to enable the efficient search for the correct temperature.
The downstream application requires the SolutionBranch of the cubic EoS to be settable; thus, the API is exposed on the ThermoPhase level.

• added setState_DP for Peng-Robinson EoS
• added Tguess for the setState_DP function
• the setForcedSolutionBranch is exposed on the ThermoPhase level

TODO

• Add test of functionality to the Peng-Robinson Testset.

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

Attention: Patch coverage is 3.70370% with 52 lines in your changes missing coverage. Please review.

Project coverage is 74.34%. Comparing base (e6f3e9d) to head (134bb71).

Files with missing lines	Patch %	Lines
src/thermo/PengRobinson.cpp	0.00%	50 Missing ⚠️
include/cantera/thermo/ThermoPhase.h	50.00%	1 Missing ⚠️
src/thermo/MixtureFugacityTP.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1847      +/-   ##
==========================================
- Coverage   74.41%   74.34%   -0.08%     
==========================================
  Files         386      386              
  Lines       53628    53679      +51     
  Branches     9063     9073      +10     
==========================================
  Hits        39905    39905              
- Misses      10652    10703      +51     
  Partials     3071     3071              

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