[SPARK-18811] StreamSource resolution should happen in stream execution thread

## What changes were proposed in this pull request?

When you start a stream, if we are trying to resolve the source of the stream, for example if we need to resolve partition columns, this could take a long time. This long execution time should not block the main thread where `query.start()` was called on. It should happen in the stream execution thread possibly before starting any triggers.

## How was this patch tested?

Unit test added. Made sure test fails with no code changes.

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #16238 from brkyvz/SPARK-18811.