Fix type checking of vector expressions

[tautschnig]

Type checking was correctly done only for some assign_* expressions,
mostly lacking support for the case of vectors + scalars.

• 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 #5812 (31f95f1) into develop (b902e0b) will decrease coverage by 0.74%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #5812      +/-   ##
===========================================
- Coverage    69.75%   69.01%   -0.75%     
===========================================
  Files         1242     1242              
  Lines       100873   100892      +19     
===========================================
- Hits         70362    69627     -735     
- Misses       30511    31265     +754     

Flag	Coverage Δ
cproversmt2	?
regression	66.72% <100.00%> (+<0.01%)	⬆️
unit	32.30% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/ansi-c/c_typecheck_expr.cpp	75.87% <100.00%> (+0.39%)	⬆️
src/goto-programs/remove_vector.cpp	98.92% <100.00%> (ø)
src/solvers/smt2/smt2irep.cpp	32.00% <0.00%> (-56.00%)	⬇️
src/solvers/smt2/smt2_conv.cpp	31.30% <0.00%> (-26.05%)	⬇️
src/solvers/floatbv/float_bv.cpp	55.33% <0.00%> (-18.84%)	⬇️
src/solvers/smt2/smt2_dec.cpp	58.82% <0.00%> (-16.18%)	⬇️
src/util/floatbv_expr.h	48.00% <0.00%> (-16.00%)	⬇️
src/solvers/flattening/pointer_logic.cpp	81.81% <0.00%> (-7.58%)	⬇️
src/util/expr_util.cpp	80.34% <0.00%> (-4.28%)	⬇️
src/solvers/smt2/smt2_format.cpp	72.41% <0.00%> (-3.45%)	⬇️
... and 11 more

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