testing/libqalculate: upgrade to 3.21.0

Subset of Changes related to library/CLI:

Ask (once) for correct interpretation of ambiguous implicit multiplication
Fix parenthesis highlighting when cursor is at end of expression
Fix initial value of interval display in preferences dialog
Fix saving of approximation mode
Improved simplification of radical expressions
Improved Im(), Re(), and arg() functions
Improved output of complex forms (other than the default rectangular) in exact mode
Function for drill bit size conversion
Fixes for equations with complex inverse trigonometric and hyperbolic functions with no solution
Fixes for complex x^(ax)=b
Minor bug fixes and feature improvements