### What changes were proposed in this pull request?
This PR intends to fix typos in the sub-modules:
* `R`
* `common`
* `dev`
* `mlib`
* `external`
* `project`
* `streaming`
* `resource-managers`
* `python`
Split per srowen https://github.com/apache/spark/pull/30323#issuecomment-728981618
NOTE: The misspellings have been reported at 706a726f87 (commitcomment-44064356)
### Why are the changes needed?
Misspelled words make it harder to read / understand content.
### Does this PR introduce _any_ user-facing change?
There are various fixes to documentation, etc...
### How was this patch tested?
No testing was performed
Closes#30402 from jsoref/spelling-R_common_dev_mlib_external_project_streaming_resource-managers_python.
Authored-by: Josh Soref <jsoref@users.noreply.github.com>
Signed-off-by: Sean Owen <srowen@gmail.com>
### What changes were proposed in this pull request?
This PR proposes to add a page to describe how to test PySpark. Note that it avoids duplication of https://spark.apache.org/developer-tools.html and it more aims to add put the relevant links together.
I made a demo site to review more effectively: https://hyukjin-spark.readthedocs.io/en/stable/development/testing.html
### Why are the changes needed?
To guide PySpark developers easily test.
### Does this PR introduce _any_ user-facing change?
Yes, it will adds a new documentation page.
### How was this patch tested?
Manually tested.
Closes#29634 from HyukjinKwon/SPARK-32783.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
