semantics change: re.all / re.allchar

[mtrberzi]

An update to the SMT-LIB strings language standard has differentiated the re.all and re.allchar operators. The semantics of these operators should be handled as follows:

• re.allchar is a regex term that matches any single character.
• re.all is a regex term that matches any string.
• These two operators are distinct, have different semantics, and cannot be substituted for each other without changing the meaning of an AST (so re.all is no longer just a different name for re.allchar).