Change *ExecutionPlan* from trait to enum similar as *LogicalPlan*

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

As #2175 mentioned, if we still keep *ExecutionPlan* as a trait, its related trait object usage will cause many limitations, like not feasible to return Self, inconvenience pattern matching, etc.

**Describe the solution you'd like**

It's better to change the *ExecutionPlan* from trait to enum similar as *LogicalPlan*. For the extension of execution plan, we can introduce a trait for that to provide some extent flexibility, like
```
enum ExecutionPlan {
...
Extension {
extension: Arc,
}
...
}
```
**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**

#2175