Add mkInteger to the API (#5274)

Add mkInteger to the API (#5274)

This PR adds mkInteger to the API and update mkReal to ensure that the returned term has real sort.
The parsers are modified to parse numbers like "0" "5" as integers and "0.0" and "15.0" as reals.
This means subtyping is effectively eliminated from all theories except arithmetic.
Other changes:

Term::isValue is removed which was introduced to support parsing for constant arrays. It is no longer needed after this PR.
Benchmarks are updated to match the changes in the parsers
Co-authored-by: Andrew Reynolds andrew-reynolds@uiowa.edu