Wrap LexRequirement, LexOrdering into their own struct

### Is your feature request related to a problem or challenge?

Currently `LexOrdering` is a type alias for `Vec`. Similarly, `LexRequirement` is a type alias for `Vec`.
I think in the long run, it is better to have something like below struct
```rust
struct LexOrdering{
inner: Vec
}
```
With this in the future we can extend the type without changing all the types.
Similar thing can be done for `LexRequirement` also.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by locating the definitions and usages of LexOrdering, LexRequirement, PhysicalSortExpr, and PhysicalSortRequirement. Review how the two aliases are constructed and passed throughout the query engine before determining the struct API. Done means both aliases are replaced without breaking their existing behavior or callers, with relevant tests still passing.

Written by the indexing model from the issue text.