Update upgrading.md for new unified config for sql string mapping to utf8view (#16809)

* Update upgrade md for new unified config for sql string mapping to utf8view

* fix formtat

* fix

* format

* Update docs/source/library-user-guide/upgrading.md

---------

Co-authored-by: Oleks V <[email protected]>

Author: zhuqi-lucas

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

@@ -120,6 +120,56 @@ SET datafusion.execution.spill_compression = 'zstd';
 
 For more details about this configuration option, including performance trade-offs between different compression codecs, see the [Configuration Settings](../user-guide/configs.md) documentation.
 
+### Deprecated `map_varchar_to_utf8view` configuration option
+
+See [issue #16290](https://github.com/apache/datafusion/pull/16290) for more information
+The old configuration
+
+```text
+datafusion.sql_parser.map_varchar_to_utf8view
+```
+
+is now **deprecated** in favor of the unified option below.\
+If you previously used this to control only `VARCHAR`→`Utf8View` mapping, please migrate to `map_string_types_to_utf8view`.
+
+---
+
+### New `map_string_types_to_utf8view` configuration option
+
+To unify **all** SQL string types (`CHAR`, `VARCHAR`, `TEXT`, `STRING`) to Arrow’s zero‑copy `Utf8View`, DataFusion 49.0.0 introduces:
+
+- **Key**: `datafusion.sql_parser.map_string_types_to_utf8view`
+- **Default**: `true`
+
+**Description:**
+
+- When **true** (default), **all** SQL string types are mapped to `Utf8View`, avoiding full‑copy UTF‑8 allocations and improving performance.
+- When **false**, DataFusion falls back to the legacy `Utf8` mapping for **all** string types.
+
+#### Examples
+
+```rust
+# /* comment to avoid running
+// Disable Utf8View mapping for all SQL string types
+let opts = datafusion::sql::planner::ParserOptions::new()
+    .with_map_string_types_to_utf8view(false);
+
+// Verify the setting is applied
+assert!(!opts.map_string_types_to_utf8view);
+# */
+```
+
+---
+
+```sql
+-- Disable Utf8View mapping globally
+SET datafusion.sql_parser.map_string_types_to_utf8view = false;
+
+-- Now VARCHAR, CHAR, TEXT, STRING all use Utf8 rather than Utf8View
+CREATE TABLE my_table (a VARCHAR, b TEXT, c STRING);
+DESCRIBE my_table;
+```
+
 ### Deprecating `SchemaAdapterFactory` and `SchemaAdapter`
 
 We are moving away from converting data (using `SchemaAdapter`) to converting the expressions themselves (which is more efficient and flexible).