[MINOR][DOCS][SQL] Fix some comments about types(TypeCoercion,Partition) and exceptions.

## What changes were proposed in this pull request?

This PR contains a few changes on code comments.
- `HiveTypeCoercion` is renamed into `TypeCoercion`.
- `NoSuchDatabaseException` is only used for the absence of database.
- For partition type inference, only `DoubleType` is considered.

## How was this patch tested?

N/A

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #13674 from dongjoon-hyun/minor_doc_types.