Support multi-residue molecules in template generator and improve performance

[epretti]

• Support multi-residue molecules, including but not limited to proteins, in template generators (resolves SMIRNOFFTempalteGenerator and proteins #415)
• Uses OpenMM's template matcher instead of NetworkX, and look up molecules by chemical formulas before trying template matching (resolves TemplateGenerator._match_residue() is too slow #426, and openmmforcefields can automatically take advantage of any future performance improvements to OpenMM template matching)
• Changes template generator cache behavior so that molecules must be specified explicitly in order to be parameterized (resolves Unexpected / unintuitive behavior of template generator caches #429)

Todo:

• Add test including multiple residues and virtual sites
• Fix CHARMM force fields updated by Templates can match whole molecules openmm#5181

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.73%. Comparing base (0551fd1) to head (8f80593).
⚠️ Report is 1 commits behind head on main.
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #430      +/-   ##
==========================================
+ Coverage   83.70%   84.73%   +1.02%     
==========================================
  Files           5        5              
  Lines         798      799       +1     
==========================================
+ Hits          668      677       +9     
+ Misses        130      122       -8     

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