Fix isSameThisPtrInConstructor for LLVM 15+ opaque pointers

[FXTi]

Fixes #1773

Rewrite isSameThisPtrInConstructor to support opaque pointer mode by:

Handling O0's alloca/store/load pattern for primary base class
Distinguishing base class (gep i8) from member field (gep %struct)
Fixing getConstructorThisPtr to handle sret attribute

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.08%. Comparing base (80c478f) to head (f992104).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1774      +/-   ##
==========================================
+ Coverage   64.00%   64.08%   +0.07%     
==========================================
  Files         244      244              
  Lines       24454    24475      +21     
  Branches     4610     4620      +10     
==========================================
+ Hits        15653    15685      +32     
+ Misses       8801     8790      -11     

Files with missing lines	Coverage Δ
svf-llvm/lib/CHGBuilder.cpp	83.62% <100.00%> (+0.11%)	⬆️
svf-llvm/lib/CppUtil.cpp	90.90% <100.00%> (+4.09%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[yuleisui]

Could you please provide your small cpp test cases regarding the fix?