[SPARK-15599][SQL][DOCS] API docs for `createDataset` functions in SparkSession

## What changes were proposed in this pull request?

Adds API docs and usage examples for the 3 `createDataset` calls in `SparkSession`

## How was this patch tested?

N/A

Author: Sameer Agarwal <sameer@databricks.com>

Closes #13345 from sameeragarwal/dataset-doc.