[SPARK-18928] Check TaskContext.isInterrupted() in FileScanRDD, JDBCRDD & UnsafeSorter

## What changes were proposed in this pull request?

In order to respond to task cancellation, Spark tasks must periodically check `TaskContext.isInterrupted()`, but this check is missing on a few critical read paths used in Spark SQL, including `FileScanRDD`, `JDBCRDD`, and UnsafeSorter-based sorts. This can cause interrupted / cancelled tasks to continue running and become zombies (as also described in #16189).

This patch aims to fix this problem by adding `TaskContext.isInterrupted()` checks to these paths. Note that I could have used `InterruptibleIterator` to simply wrap a bunch of iterators but in some cases this would have an adverse performance penalty or might not be effective due to certain special uses of Iterators in Spark SQL. Instead, I inlined `InterruptibleIterator`-style logic into existing iterator subclasses.

## How was this patch tested?

Tested manually in `spark-shell` with two different reproductions of non-cancellable tasks, one involving scans of huge files and another involving sort-merge joins that spill to disk. Both causes of zombie tasks are fixed by the changes added here.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #16340 from JoshRosen/sql-task-interruption.

(cherry picked from commit 5857b9ac)
Signed-off-by: Herman van Hovell <hvanhovell@databricks.com>