Correctly print sp.Abs in generated code

Another issue reported by @alexander.reinauer.

There was a reason for writing the absolute value as a ternary expression. I don't think we can assume the fabs function to be always available.

When the CI pipeline is fixed, I'll run the large testsuite with lbmpy and pygrandchem with this MR

Right now it just prints Abs instead of fabs/abs, which is obviously wrong.

Originally, we used the Sympy printer which used the correct function name but printer the arguments wrongly: e.g. abs(cast_func(1, double)) instead of abs(1.0). Now we have Abs(1.0) (would be fixed by this PR)).

added 81 commits

• 659319bd...a5ab1070 - 80 commits from branch master
• b1e9b1e4 - Merge branch 'master' of i10git.cs.fau.de:pycodegen/pystencils into abs

Compare with previous version

The integration tests with lbmpy and pygrandchem completed just fine.

merged

mentioned in commit 54bd44ef