Update cplex solution parser for cplex 12.10

[jsiirola]

Fixes #1766

Summary/Motivation:

Starting in CPLEX 12.10, cplex returns an <objectiveValues> tag as part of the solution output. This was running afoul of the sol file parser. This is an extension of PR #1779 to actually parse and return the named objective values in the results object.

Changes proposed in this PR:

• parse the <objectiveValues> / <objective> tags in the cplex output
• update kernel.block.load_solution() to not throw errors when redundant objective values are encountered.

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1. I agree my contributions are submitted under the BSD license.
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[codecov]

Codecov Report

Merging #1792 (49b20dc) into master (dcd3fd8) will decrease coverage by 0.20%.
The diff coverage is 37.50%.

@@            Coverage Diff             @@
##           master    #1792      +/-   ##
==========================================
- Coverage   74.95%   74.75%   -0.21%     
==========================================
  Files         638      638              
  Lines       91797    92837    +1040     
==========================================
+ Hits        68810    69400     +590     
- Misses      22987    23437     +450     

Impacted Files	Coverage Δ
pyomo/solvers/plugins/solvers/CPLEX.py	88.01% <28.57%> (-0.78%)	⬇️
pyomo/core/kernel/block.py	100.00% <100.00%> (ø)
pyomo/solvers/plugins/solvers/GUROBI.py	68.50% <0.00%> (-21.24%)	⬇️
pyomo/solvers/plugins/solvers/GAMS.py	71.41% <0.00%> (-6.37%)	⬇️
pyomo/contrib/gdpbb/GDPbb.py	19.84% <0.00%> (-1.87%)	⬇️
pyomo/contrib/mindtpy/MindtPy.py	97.10% <0.00%> (-1.28%)	⬇️
pyomo/repn/plugins/gams_writer.py	92.98% <0.00%> (-0.26%)	⬇️
pyomo/solvers/plugins/solvers/mosek_direct.py	13.27% <0.00%> (-0.02%)	⬇️
pyomo/contrib/gdpopt/GDPopt.py	100.00% <0.00%> (ø)
pyomo/contrib/multistart/multi.py	100.00% <0.00%> (ø)
... and 4 more

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