Infer conflicts based on regular expression inclusion (#3234)

Infer conflicts based on regular expression inclusion (#3234)

We have a conflict if we have `str.in.re(x, R1)` and `~str.in.re(x, R2)`
and `R2` includes `R1` because there is no possible value for `x` that
satisfies both memberships. This commit adds code to detect regular
expression inclusion for a small fragment of regular expressions: string
literals with single char (`re.allchar`) and multichar wildcards
(`re.*(re.allchar)`).

Signed-off-by: Andres Noetzli <anoetzli@amazon.com>