Value sets: fix byte extracts from structs

[tautschnig]

Pointers may be contained in any member that's included in the byte
range being extracted, not just the one right at the offset that the
byte extract starts from.

Co-Authored-By: Petr Bauch petr.bauch@gmail.com

• 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

Merging #6107 (6ac8ebb) into develop (4c14789) will increase coverage by 0.08%.
The diff coverage is 96.96%.

@@             Coverage Diff             @@
##           develop    #6107      +/-   ##
===========================================
+ Coverage    74.52%   74.60%   +0.08%     
===========================================
  Files         1447     1447              
  Lines       157808   157825      +17     
===========================================
+ Hits        117610   117752     +142     
+ Misses       40198    40073     -125     

Impacted Files	Coverage Δ
src/pointer-analysis/value_set.cpp	81.14% <93.75%> (-1.48%)	⬇️
src/solvers/flattening/boolbv_index.cpp	89.72% <100.00%> (+10.77%)	⬆️
src/solvers/smt2/smt2_conv.cpp	60.63% <0.00%> (+0.22%)	⬆️
src/solvers/lowering/byte_operators.cpp	92.16% <0.00%> (+0.36%)	⬆️
src/ansi-c/c_typecast.cpp	79.00% <0.00%> (+0.55%)	⬆️
src/util/pointer_offset_size.cpp	86.79% <0.00%> (+1.07%)	⬆️
src/solvers/flattening/boolbv_byte_extract.cpp	82.27% <0.00%> (+12.65%)	⬆️
src/solvers/floatbv/float_bv.cpp	88.33% <0.00%> (+14.47%)	⬆️

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[NlightNFotis]

LGTM