Add sign extension assignment operator

[sylvainpelissier]

Checklist

• Closing issues: #issue
• Mark this if you consider it ready to merge
• I've added tests (optional)
• I wrote some lines in the radare2book

Description

Introduce new ~= operator doing sign extension assignment of a register. For example:

> "ae 0x81,a0,="
> "ae 8,a0,~="
> ar a0
0xffffff81

This would simplify a lot of ESIL expressions for architecture using sign extension.

[trufae]

Ideally it will be good to share most code with esil_signext, can you refactor this? we should be able to describe operations in a functional way without having to go into much details in the code. X= operations must be calling internally the X operation and then the = operation for example.

[sylvainpelissier]

I refactored to share code but doing that in a functional way is not obvious to me.

[codecov-io]

Codecov Report

Merging #18092 (1776c1c) into master (15d8de3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #18092   +/-   ##
=======================================
  Coverage   41.75%   41.75%           
=======================================
  Files        1078     1078           
  Lines      351288   351297    +9     
=======================================
+ Hits       146678   146687    +9     
  Misses     204610   204610           

Impacted Files	Coverage Δ
libr/anal/esil.c	76.03% <100.00%> (+0.09%)	⬆️

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