### What changes were proposed in this pull request?
This PR proposes migration of [`pyspark-stubs`](https://github.com/zero323/pyspark-stubs) into Spark codebase.
### Why are the changes needed?
### Does this PR introduce _any_ user-facing change?
Yes. This PR adds type annotations directly to Spark source.
This can impact interaction with development tools for users, which haven't used `pyspark-stubs`.
### How was this patch tested?
- [x] MyPy tests of the PySpark source
```
mypy --no-incremental --config python/mypy.ini python/pyspark
```
- [x] MyPy tests of Spark examples
```
MYPYPATH=python/ mypy --no-incremental --config python/mypy.ini examples/src/main/python/ml examples/src/main/python/sql examples/src/main/python/sql/streaming
```
- [x] Existing Flake8 linter
- [x] Existing unit tests
Tested against:
- `mypy==0.790+dev.e959952d9001e9713d329a2f9b196705b028f894`
- `mypy==0.782`
Closes#29591 from zero323/SPARK-32681.
Authored-by: zero323 <mszymkiewicz@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
### What changes were proposed in this pull request?
change PySpark ml ```Params._clear``` to ```Params.clear```
### Why are the changes needed?
PySpark ML currently has a private _clear() method that will unset a param. This should be made public to match the Scala API and give users a way to unset a user supplied param.
### Does this PR introduce any user-facing change?
Yes. PySpark ml ```Params._clear``` ---> ```Params.clear```
### How was this patch tested?
Add test.
Closes#26130 from huaxingao/spark-29464.
Authored-by: Huaxin Gao <huaxing@us.ibm.com>
Signed-off-by: Bryan Cutler <cutlerb@gmail.com>
## What changes were proposed in this pull request?
This PR breaks down the large ml/tests.py file that contains all Python ML unit tests into several smaller test files to be easier to read and maintain.
The tests are broken down as follows:
```
pyspark
├── __init__.py
...
├── ml
│ ├── __init__.py
...
│ ├── tests
│ │ ├── __init__.py
│ │ ├── test_algorithms.py
│ │ ├── test_base.py
│ │ ├── test_evaluation.py
│ │ ├── test_feature.py
│ │ ├── test_image.py
│ │ ├── test_linalg.py
│ │ ├── test_param.py
│ │ ├── test_persistence.py
│ │ ├── test_pipeline.py
│ │ ├── test_stat.py
│ │ ├── test_training_summary.py
│ │ ├── test_tuning.py
│ │ └── test_wrapper.py
...
├── testing
...
│ ├── mlutils.py
...
```
## How was this patch tested?
Ran tests manually by module to ensure test count was the same, and ran `python/run-tests --modules=pyspark-ml` to verify all passing with Python 2.7 and Python 3.6.
Closes#23063 from BryanCutler/python-test-breakup-ml-SPARK-26033.
Authored-by: Bryan Cutler <cutlerb@gmail.com>
Signed-off-by: hyukjinkwon <gurwls223@apache.org>
