Add support for complementarity constraints

[frapac]

This PR is an attempt to support complementarity constraints, following #37

It introduces three modifications:

• the number of complementarity constraints n_cc and positions cvar are imported from Ampl using asl_n_cc and asl_cvar, respectively.
• both n_cc and cvar are stored in AmplNLPMeta
• a wrapper AmplMPECModel implements a smooth reformulation of the complementarity constraints.

The constraints

x_L <= x complements g(x) >= g_L 

is reformulated as

x_L <= x 
g_L <= g(x)
Diag(g(x)) * x <= 0 

We can think of implementing other smooth reformulations.

AmplMPECModel adds some complexity to the package, and it could be appropriate to move this wrapper in a second package once NLPModels has a proper support for complementarity constraints.

Cc @tmigot @dpo

[amontoison]

@frapac Can you rebase your branch?

[codecov]

Codecov Report

Attention: Patch coverage is 95.43568% with 11 lines in your changes missing coverage. Please review.

Project coverage is 87.83%. Comparing base (7470bdf) to head (0d8d8a7).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ampl_mpec_model.jl	96.12%	9 Missing ⚠️
src/ampl_model.jl	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #144      +/-   ##
==========================================
+ Coverage   82.68%   87.83%   +5.14%     
==========================================
  Files           3        3              
  Lines         335      567     +232     
==========================================
+ Hits          277      498     +221     
- Misses         58       69      +11     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.