Update 53 upgrade guide to note release, other changes (#21449)

## Which issue does this PR close?

- Related to #19692

## Rationale for this change

@rluvaton noted some issues with the 53 upgrade guide
#19692 (comment):

> FYI, the migration guide says 53.0.0 was not released yet and it miss
the following breaking changes:
> 
> #20319 - removed deprecated
function from ExecutionPlan trait
> #19635 - added argument to
HashJoinExec::try_new function

## What changes are included in this PR?

Fix the above

## Are these changes tested?
Yes by CI

## Are there any user-facing changes?

Better docs

Author: alamb

docs/source/library-user-guide/upgrading/53.0.0.md

@@ -21,13 +21,6 @@
 
 ## DataFusion 53.0.0
 
-**Note:** DataFusion `53.0.0` has not been released yet. The information provided
-*in this section pertains to features and changes that have already been merged
-*to the main branch and are awaiting release in this version. See [#19692] for
-\*more details.
-
-[#19692]: https://github.com/apache/datafusion/issues/19692
-
 ### Upgrade arrow/parquet to 58.0.0 and object_store to 0.13.0
 
 DataFusion 53.0.0 uses `arrow` and `parquet` 58.0.0, and `object_store` 0.13.0.
@@ -39,6 +32,39 @@ See the [Arrow 58.0.0 release notes] and the [object_store 0.13.0 upgrade guide]
 [arrow 58.0.0 release notes]: https://github.com/apache/arrow-rs/releases/tag/58.0.0
 [object_store 0.13.0 upgrade guide]: https://github.com/apache/arrow-rs-object-store/blob/v0.13.0/CHANGELOG.md
 
+### `ExecutionPlan::statistics` removed
+
+The deprecated `ExecutionPlan::statistics()` method has been removed. If you
+implement custom `ExecutionPlan`s, remove that method from your impl and
+implement `partition_statistics()` instead.
+
+**Before:**
+
+```rust,ignore
+impl ExecutionPlan for MyExec {
+    // ...
+
+    fn statistics(&self) -> Result<Statistics> {
+        Ok(Statistics::new_unknown(&self.schema()))
+    }
+}
+```
+
+**After:**
+
+```rust,ignore
+impl ExecutionPlan for MyExec {
+    // ...
+
+    fn partition_statistics(&self, _partition: Option<usize>) -> Result<Statistics> {
+        Ok(Statistics::new_unknown(&self.schema()))
+    }
+}
+```
+
+If you do not have partition-specific statistics, return the same value for
+`None` and for any partition index.
+
 ### `ExecutionPlan::properties` now returns `&Arc<PlanProperties>`
 
 Now `ExecutionPlan::properties()` returns `&Arc<PlanProperties>` instead of a
@@ -125,6 +151,15 @@ let sub_plan = self.query_to_plan(subquery, planner_context)?;
 planner_context.pop_outer_query_schema();
 ```
 
+### `HashJoinExec::try_new` adds `null_aware`
+
+`HashJoinExec::try_new` now takes an extra `null_aware: bool` argument. This
+flag is used for null-aware anti joins, such as plans generated for `NOT IN`
+subqueries.
+
+Most callers should pass `false`, the previous behavior. Pass `true` only for null-aware
+`JoinType::LeftAnti` joins.
+
 ### `FileSinkConfig` adds `file_output_mode`
 
 `FileSinkConfig` now includes a `file_output_mode: FileOutputMode` field to control