[CONTRACTS] Support for Kani Loop Contracts

[qinheping]

This PR add support for Kani loop contracts introduced in model-checking/kani#3151. It adds

1. a new flag to goto-instrument to enable kani loop contracts.
2. new instrumentation rules for loop contracts annotated by Kani.
3. and helper functions to extract loop contracts from goto model generated by Kani.

As this feature is specified to GOTO generated by Kani, it is not clear to me how to test it along without Kani.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Attention: Patch coverage is 20.58824% with 81 lines in your changes are missing coverage. Please review.

Project coverage is 78.25%. Comparing base (03f604e) to head (af195ba).
Report is 11 commits behind head on develop.

Files	Patch %	Lines
src/goto-instrument/contracts/utils_kani.cpp	0.00%	57 Missing ⚠️
src/goto-instrument/contracts/contracts.cpp	34.28%	23 Missing ⚠️
.../goto-instrument/goto_instrument_parse_options.cpp	90.00%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## develop #8260 +/- ##
===========================================
- Coverage 79.66% 78.25% -1.42% 
===========================================
Files 1683 1721 +38 Lines 195713 188315 -7398 Branches 0 18484 +18484 ===========================================
- Hits 155913 147361 -8552 - Misses 39800 40954 +1154 

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[tautschnig]

As discussed out-of-band: we need to find a way to fully do this in Kani.