Summary:
Tests a scenario where range tombstone reseek used to cause MergingIterator to discard non-ok status.

Ran on main without https://github.com/facebook/rocksdb/issues/11786:
```
./db_range_del_test --gtest_filter="*RangeDelReseekAfterFileReadError*"
Note: Google Test filter = *RangeDelReseekAfterFileReadError*
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from DBRangeDelTest
[ RUN      ] DBRangeDelTest.RangeDelReseekAfterFileReadError
db/db_range_del_test.cc:3577: Failure
Value of: iter->Valid()
  Actual: true
Expected: false
[  FAILED  ] DBRangeDelTest.RangeDelReseekAfterFileReadError (64 ms)
```

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11790

Reviewed By: ajkr

Differential Revision: D48972869

Pulled By: cbi42

fbshipit-source-id: b1a71867533b0fb60af86f8ce8a9e391ba84dd57