Don't recheck existence of files when generating File Relation resolution in StructuredStreaming

Structured Streaming's FileSource lists files to classify files as Offsets. Once this file list is committed to a metadata log for a batch, this file list is turned into a "Batch FileSource" Relation which acts as the source to the incremental execution.

While this "Batch FileSource" Relation is resolved, we re-check that every single file exists on the Driver. It takes a horrible amount of time, and is a total waste. We can simply skip file existence during execution.