Public some projected methods in FileScanConfig

[xudong963]

Which issue does this PR close?

• Closes #.

Rationale for this change

While upgrading DF46, I found tthat hese methods aren't public, but under some scenes, we may only need the projected schema or another, so it's not efficient to call project() method, which returns four elements

pub fn project(&self) -> (SchemaRef, Constraints, Statistics, Vec<LexOrdering>) {
        if self.projection.is_none() && self.table_partition_cols.is_empty() {
            return (
                Arc::clone(&self.file_schema),
                self.constraints.clone(),
                self.file_source.statistics().unwrap().clone(),
                self.output_ordering.clone(),
            );
        }

        let schema = self.projected_schema();
        let constraints = self.projected_constraints();
        let stats = self.projected_stats();

        let output_ordering = get_projected_output_ordering(self, &schema);

        (schema, constraints, stats, output_ordering)
    }

What changes are included in this PR?

Make the three projected methods public

Are these changes tested?

Are there any user-facing changes?

[alamb]

Thanks @xudong963 and @jayzhan211