bv_typet is also sensitive to endianness

[tautschnig]

The bits within an object of bv_typet are ordered depending on
endianness. This is consistent with typecasts to/from bv_typet of some
other bitvector type, which do not alter the sequence of bits.

• 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.

[peterschrammel]

Have you got a test case that exhibited this problem?

[tautschnig]

Have you got a test case that exhibited this problem?

Currently in the last three commits in #6442. I'll seek to move them over here in case they pass with just the changes in here. There are a lot more changes in the last commit in #6442 ...

[codecov]

Codecov Report

Merging #6485 (5bf69a3) into develop (f5789d0) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #6485   +/-   ##
========================================
  Coverage    76.04%   76.04%           
========================================
  Files         1546     1546           
  Lines       165485   165521   +36     
========================================
+ Hits        125836   125864   +28     
- Misses       39649    39657    +8     

Impacted Files	Coverage Δ
src/solvers/lowering/byte_operators.cpp	92.21% <100.00%> (-0.03%)	⬇️
src/util/endianness_map.cpp	62.06% <100.00%> (-14.60%)	⬇️
unit/solvers/lowering/byte_operators.cpp	100.00% <100.00%> (ø)

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[tautschnig]

Have you got a test case that exhibited this problem?

Currently in the last three commits in #6442. I'll seek to move them over here in case they pass with just the changes in here. There are a lot more changes in the last commit in #6442 ...

Test added and commit message amended to explain what was failing before.