Refactor simplify_expressions and expr_simplifier

[HaoYang670]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Currently, the items related to expression simplification are in simplification_expressions.rs and expr_simplifier, which is somewhat messy.
Some structs such as ConstEvaluator and Simplifier are only used in the simplification_expr, but are public in datafusion_optimizer.

Also, there are some util functions that we should also clean them up.

Describe the solution you'd like
I'd like to create a new mod and put all the things above in it.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.