[VL] chartype cause projectexec fallback with spark3.4

### Backend

VL (Velox)

### Bug description

In spark3.4, because of the patch https://issues.apache.org/jira/browse/SPARK-40697, gluten can not transform ProjectExec including chartype columns to native, maybe we should add this to Limitation.doc or recommand users to disable `spark.sql.readSideCharPadding`

### Spark version

None

### Spark configurations

_No response_

### System information

_No response_

### Relevant logs

_No response_

Start by reviewing Limitation.doc and the Spark 3.4 context described in SPARK-40697, then check how the spark.sql.readSideCharPadding setting relates to the reported fallback. Done means documenting the limitation or clearly recommending that users disable the setting, with the affected chartype case explained.

Written by the indexing model from the issue text.