[CONTRACTS] Allow loop contracts annotated to goto statement

[qinheping]

This PR enable loop contracts annotated to goto statement, which is we we do in Kani generated GOTO program.

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[tautschnig]

Nobody reads warnings. Can you describe the scenario where side effects would be ok?

[qinheping]

According to the offline discussion. I will move all the checks and throw to contracts component. They should not be in the converter.

[qinheping]

This PR now only allow loop contracts annotated to GOTO. Check for side effect will be in another PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.37%. Comparing base (8646bfa) to head (d2f185f).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8281      +/-   ##
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- Coverage    78.37%   78.37%   -0.01%     
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  Files         1726     1726              
  Lines       188322   188324       +2     
  Branches     18460    18484      +24     
===========================================
+ Hits        147606   147607       +1     
- Misses       40716    40717       +1     

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