Field sensitivity: account for array size in all index expressions

[tautschnig]

When code outside the core field-sensitivity implementation produces index expressions we must not blindly turn such expressions into ssa_exprt.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a 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).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

❌ Patch coverage is 93.61702% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.46%. Comparing base (06665e7) to head (bf5d793).
⚠️ Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/goto-symex/field_sensitivity.cpp	93.61%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8579   +/-   ##
========================================
  Coverage    80.46%   80.46%           
========================================
  Files         1698     1698           
  Lines       208510   208523   +13     
  Branches        73       73           
========================================
+ Hits        167784   167798   +14     
+ Misses       40726    40725    -1     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.