introduce update_bit_exprt

[kroening]

This adds update_bit_exprt, for a single-bit update, analogously to extractbit and extractbits.

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• 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).
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[codecov]

Codecov Report

Attention: 58 lines in your changes are missing coverage. Please review.

Comparison is base (547b1a8) 79.68% compared to head (6925475) 79.66%.

Files	Patch %	Lines
src/util/bitvector_expr.h	0.00%	21 Missing ⚠️
src/util/bitvector_expr.cpp	0.00%	14 Missing ⚠️
src/solvers/flattening/boolbv_with.cpp	0.00%	12 Missing ⚠️
src/solvers/smt2/smt2_conv.cpp	11.11%	8 Missing ⚠️
src/solvers/flattening/boolbv_update_bit.cpp	0.00%	2 Missing ⚠️
src/solvers/flattening/boolbv.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8190      +/-   ##
===========================================
- Coverage    79.68%   79.66%   -0.03%     
===========================================
  Files         1681     1682       +1     
  Lines       195319   195375      +56     
===========================================
+ Hits        155636   155639       +3     
- Misses       39683    39736      +53     

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[peterschrammel]

It would be great to have a test that actually uses that - at least in hw-cbmc.

[kroening]

It would be great to have a test that actually uses that - at least in hw-cbmc.

Coming. This is a bit of a chicken-and-egg problem.