Fix 4689 Exclude ThreadPoolExecutor and ProcessPoolExecutor from consider-using-with

[DudeNr33]

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Description

This PR addresses two issues:

• Completely exclude ThreadPoolExecutor and ProcessPoolExecutor from consider-using-with, as consider-using-with on ThreadPoolExecutor? #4689 points out that legitimate use cases exist where they are used without a with block.
• Check if a context manager that was assigned to a variable is used later on in a with block. Therefore, the following (although unusual, there are probably better examples for this) will no longer emit a consider-using-with message:

file_handle = open("foo")  # formerly triggered ``consider-using-with``, not anymore now
with file_handle:
    content = file_handle.read()

Type of Changes

	Type
✓	🐛 Bug fix
✓	🔨 Refactoring

Related Issue

Closes #4689

[coveralls]

Coverage increased (+0.03%) to 92.09% when pulling 42132f5 on DudeNr33:fix-4689-threadpoolexecutor into f437752 on PyCQA:main.

[Pierre-Sassoulas]

Thank you for taking the time to fix the false positive for this checker and participating in the issue related to it, much appreciated ! I made some suggestion feel free to ignore if it's not relevant.

[DudeNr33]

Thanks for the review, I will implement the suggested changes (but only tomorrow).
Especially the __iter__ and a clear (or clear_all) method are nice improvements.

[Pierre-Sassoulas]

Thanks for the fix ! This was the last MR for pylint 2.9.4 I'm going to release it now :)