CONTRACTS: use alias analysis to infer loop assigns in synthesizer

[qinheping]

This PR contains two changes.

First, we will no longer error out when the alias analysis fails when we infer loop assigns. When the local alias analysis fails on some pointers, it still probably success on other pointers. So it is worth to return whatever assigns targets inferred.

Second, we will use local alias analysis to infer initial loop assigns during loop-contracts synthesis. The synthesizer currently uses traces reported by CBMC to construct assigns targets from counterexamples. It can construct at more one assigns target for one call to CBMC. One run of local alias analysis is faster than one run of CBMC, and can infer more than one assigns targets. Therefore, using local alias analysis can improve the performance of the synthesizer.

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (37d57b3) 78.51% compared to head (c5bebfa) 78.50%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7603      +/-   ##
===========================================
- Coverage    78.51%   78.50%   -0.01%     
===========================================
  Files         1670     1670              
  Lines       191787   191795       +8     
===========================================
- Hits        150574   150567       -7     
- Misses       41213    41228      +15     

Impacted Files	Coverage Δ
src/goto-instrument/loop_utils.cpp	83.78% <100.00%> (ø)
...hesizer/enumerative_loop_contracts_synthesizer.cpp	96.19% <100.00%> (+0.13%)	⬆️
...nthesizer/enumerative_loop_contracts_synthesizer.h	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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