[SQL] Improve Query Validation

In couple of places we don't validate the query and crash with some low-level non-informative exceptions.

For example, when there's different number of fields in SELECT than in the RowCoder of the result in PAssert, then we will throw EOF exception trying to decode the result, instead of providing meaningful description of what's wrong.

We need to implement additional validation in such cases.

Imported from Jira [BEAM-3712](https://issues.apache.org/jira/browse/BEAM-3712). Original Jira may contain additional context.
Reported by: kedin.

Start with the SQL validation and PAssert/RowCoder paths described in the issue, using the mismatched SELECT-field and result-RowCoder example as the first case to trace. Done means this mismatch is validated before decoding and reports a meaningful query error instead of an EOF exception; consult BEAM-3712 for the imported context.

Written by the indexing model from the issue text.