Includes several fixes found during testing:
A check to avoid assertion failure in the flex parser
Changes atomic SEXPR to symbols instead of constant strings to avoid spurious error messages for non-standard characters
Changes to options configuration for Flex for performance (as a result, this does not fix check-synth doesn't flush output #9257).
Fix for --stdin-input-per-line to not set incremental by default for non-interactive inputs.
Note that TPTP parsing still uses the ANTLR parser.
Fixes#9258.
Fixes#8374.
Fixes#1862.
Fixes#791.
Fixescvc5/cvc5-wishues#142.
