Move physical_plan::file_format to datasource::plan

[alamb]

Which issue does this PR close?

This is part of #1754

Rationale for this change

While trying to extract physical_plan out of the core datafusion crate, the implementation of the various formats need to instantiate ExecutionPlans (e.g. ParquetExec) -- so therefore I conclude I need to remove the dependency out of physical_plan

What changes are included in this PR?

1. Move physical_plan::file_format to datasource::physical_plan

Are these changes tested?

Existing tests

Are there any user-facing changes?

Yes, this does change the import path for anyone who uses structures like ParquetExec, etc

from

use crate::physical_plan::file_format::{ParquetExec, FileScanConfig};

To

use crate::datasource::physical_plan::{ParquetExec, FileScanConfig};

I would be open to other suggestions too.

Sorry in advance

[alamb]

After a bunch of thought, I am convinced this is the right next step towards splitting out physical plan

Thus I plan to update and merge this PR after #6526 from @mustafasrepo is merged

[alamb]

I think after this PR I can move physical_plan out of datafusion core

I will then work on extracting datafusion_physical_optimizer out as well

[alamb]

Since this has a substantial chance of conflicts I am going to merge it in now to avoid them as much as possible