fix: decode invalid UTF-8 at the JVM to native FFI import boundary

docs/source/user-guide/latest/compatibility/scans.md

@@ -67,9 +67,11 @@ The following limitations raise an error at scan time rather than falling back t
   Arrow, whose string type is strictly UTF-8. Reading a Parquet file whose `STRING` column contains
   non-UTF-8 bytes fails with `Parquet error: encountered non UTF-8 data`. Disable Comet for the
   query, or cast the column to `BINARY` before persisting, if you need to preserve non-UTF-8 bytes.
-  Separately, non-UTF-8 bytes that reach native execution from a JVM-side columnar source are not
-  currently validated at the Arrow FFI import boundary. See [#4121](https://github.com/apache/datafusion-comet/issues/4121)
-  and the tracking issue [#4764](https://github.com/apache/datafusion-comet/issues/4764).
+  By contrast, Comet decodes non-UTF-8 bytes from JVM-side columnar sources at the Arrow FFI import
+  boundary using JVM-compatible replacement semantics. See
+  [Strings with non-UTF-8 bytes](index.md#strings-with-non-utf-8-bytes),
+  [#4121](https://github.com/apache/datafusion-comet/issues/4121), and the tracking issue
+  [#4764](https://github.com/apache/datafusion-comet/issues/4764).
 - Reading `TimestampLTZ` as `TimestampNTZ` on Spark 3.x. Spark raises an error per
   [SPARK-36182](https://issues.apache.org/jira/browse/SPARK-36182) because LTZ encodes UTC-adjusted
   instants that cannot be safely reinterpreted as timezone-free values, and Comet matches this by

native/common/src/lib.rs

@@ -19,9 +19,11 @@ mod error;
 mod query_context;
 mod schema;
 pub mod tracing;
+mod utf8;
 mod utils;
 
 pub use error::{decimal_overflow_error, SparkError, SparkErrorWithContext, SparkResult};
 pub use query_context::{create_query_context_map, QueryContext, QueryContextMap};
 pub use schema::{cast_and_stamp_schema, widen_nested_nullability};
+pub use utf8::decode_string_arrays;
 pub use utils::{bytes_to_i128, decode_utf8_spark_lossy};