## What changes were proposed in this pull request?

This PR deals with four points as below:

- Reuse existing DDL parser APIs rather than reimplementing within PySpark

- Support DDL formatted string, `field type, field type`.

- Support case-insensitivity for parsing.

- Support nested data types as below:

  **Before**
  ```
  >>> spark.createDataFrame([[[1]]], "struct<a: struct<b: int>>").show()
  ...
  ValueError: The strcut field string format is: 'field_name:field_type', but got: a: struct<b: int>
  ```

  ```
  >>> spark.createDataFrame([[[1]]], "a: struct<b: int>").show()
  ...
  ValueError: The strcut field string format is: 'field_name:field_type', but got: a: struct<b: int>
  ```

  ```
  >>> spark.createDataFrame([[1]], "a int").show()
  ...
  ValueError: Could not parse datatype: a int
  ```

  **After**
  ```
  >>> spark.createDataFrame([[[1]]], "struct<a: struct<b: int>>").show()
  +---+
  |  a|
  +---+
  |[1]|
  +---+
  ```

  ```
  >>> spark.createDataFrame([[[1]]], "a: struct<b: int>").show()
  +---+
  |  a|
  +---+
  |[1]|
  +---+
  ```

  ```
  >>> spark.createDataFrame([[1]], "a int").show()
  +---+
  |  a|
  +---+
  |  1|
  +---+
  ```

## How was this patch tested?

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #18590 from HyukjinKwon/deduplicate-python-ddl.