File source v2 should validate data schema only

Currently, File source v2 allows each data source to specify the supported data types by implementing the method `supportsDataType` in `FileScan` and `FileWriteBuilder`.

However, in the read path, the validation checks all the data types in `readSchema`, which might contain partition columns. This is actually a regression. E.g. Text data source only supports String data type, while the partition columns can still contain Integer type since partition columns are processed by Spark.

This PR is to:
1. Refactor schema validation and check data schema only
2. Filter the partition columns in data schema if user specified schema provided.