SMT2 back-end: make declare-datatypes standards compatible

[tautschnig]

The standards-compatible syntax is understood by both Z3 (which also accepted the previous one) as well as CVC5 (which only accepts the new one).

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[kroening]

Do you happen to know which version of Z3 added support for the new one?
We should communicate a set of supported solver versions.

[codecov]

Codecov Report

Merging #7145 (5bbb238) into develop (3034749) will not change coverage.
The diff coverage is 33.33%.

@@           Coverage Diff            @@
##           develop    #7145   +/-   ##
========================================
  Coverage    77.87%   77.87%           
========================================
  Files         1576     1576           
  Lines       181824   181824           
========================================
  Hits        141598   141598           
  Misses       40226    40226           

Impacted Files	Coverage Δ
src/solvers/smt2/smt2_conv.cpp	68.69% <33.33%> (ø)

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[tautschnig]

Do you happen to know which version of Z3 added support for the new one? We should communicate a set of supported solver versions.

I have only tested with version 4.8.7 (has been released 2019-11-19) on my system, I wasn't aware that support for this varied over time.

[martin-cs]

Useful; thank you.

[martin-cs]

Do you happen to know which version of Z3 added support for the new one? We should communicate a set of supported solver versions.

I have only tested with version 4.8.7 (has been released 2019-11-19) on my system, I wasn't aware that support for this varied over time.

Datatypes were only added to the standard SMT-LIB in 2.6, so July 2017. They were supported by a number of solvers long before that but with varying syntax.

[martin-cs]

This fails the coverage test but I think that is more due to limitations of our testing of the SMT-LIB back-end than anything to do with this patch so I am merging it.