[Kernel][Writes] Add support for writing data file stats

[raveeram-db]

Which Delta project/connector is this regarding?

• [ ] Spark
• [ ] Standalone
• [ ] Flink
• [x] Kernel
• [ ] Other (fill in here)

Description

Serializes stats to the data file on writes.

How was this patch tested?

Unit tests.

Does this PR introduce any user-facing changes?

No

[raveeram-db]

Will fix the tests.

[raveeram-db]

Looks great! Left only a few minor comments / questions.

Seems like we need some tests for DEFAULT_DATA_SKIPPING_NUM_INDEXED_COLS and, in particular, need to test + document the expected behavior for how nested columns impact the total column count.

Thanks @scottsand-db , added a test and a clarifying comment for the same