Improve performance of pyomo.dae

[blnicho]

Summary/Motivation:

This PR removes unnecessary calls to sorted in Pyomo.DAE and replaces usage of <list>.index() with <ContinuousSet>.ord(). With these two minor changes the time to apply the discretization transformation is nearly halved on some large test problems. These changes were motivated by the profiling data in #1157.

Changes proposed in this PR:

• remove calls to sorted in Pyomo.DAE
• use ord instead of index for locating elements in a ContinuousSet

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

Merging #1727 (7782d0d) into master (b00dc2b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1727   +/-   ##
=======================================
  Coverage   71.28%   71.29%           
=======================================
  Files         631      631           
  Lines       91056    91047    -9     
=======================================
  Hits        64909    64909           
+ Misses      26147    26138    -9     

Impacted Files	Coverage Δ
pyomo/dae/contset.py	98.95% <100.00%> (ø)
pyomo/dae/misc.py	93.75% <100.00%> (ø)
pyomo/dae/plugins/colloc.py	99.14% <100.00%> (+2.20%)	⬆️
pyomo/dae/plugins/finitedifference.py	96.15% <100.00%> (ø)
pyomo/network/foqus_graph.py	90.54% <0.00%> (+0.23%)	⬆️

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[michaelbynum]

Nice! That was fast.