implement tree explain for CoalesceBatchesExec (apache#15194)

* feat: implement tree explain for CoalesceBatchesExec

Signed-off-by: Alan Tang <[email protected]>

* chore: only fix on tree rendering

Signed-off-by: Alan Tang <[email protected]>

* feat(test): Add tree rendering test for CoalesceBatchesExec with a limit

Signed-off-by: Alan Tang <[email protected]>

---------

Signed-off-by: Alan Tang <[email protected]>
Co-authored-by: Andrew Lamb <[email protected]>

Author: Standing-Man

datafusion/physical-plan/src/coalesce_batches.rs

@@ -123,8 +123,11 @@ impl DisplayAs for CoalesceBatchesExec {
                 Ok(())
             }
             DisplayFormatType::TreeRender => {
-                // TODO: collect info
-                write!(f, "")
+                writeln!(f, "target_batch_size={}", self.target_batch_size)?;
+                if let Some(fetch) = self.fetch {
+                    write!(f, "limit={fetch}")?;
+                };
+                Ok(())
             }
         }
     }