Most importantly, the means Python 2.7 no longer needs to get supported

* All of them are removed from the package distributions
* Scripts is additionally moved to the cpdf project
* Sample_Code is moved to the docs

PdfFileReader and PdfFileMerger no longer have the `overwriteWarnings`.
The new behavior is `overwriteWarnings=False`.

Additionally, PyPDF2.utils.formatWarning was removed

Closes #829

It's expected that this is a more sensible default for most users.

As support for Python 3.5 and lower was dropped, we can use more modern syntax

This includes adding a type m

In case of invalid extract stream data looking for endstream

Closes #301

This PR uses 4 ways to disable checks by mypy:

*  74x `typing.cast`: Has no effect on the running code, just on mypy
* 161x `typing.Any`: If we tell mypy that a parameter / variable can have any possible type, mypy cannot check anything.
*  82x `# type: ignore`
*  36x `assert foo is not None`: This can have an effect in running code and should only be used if mypy fails to understand that foo is guaranteed not to be None

Those are especially necessary for `.getObject()` calls. If possible, they
should be removed.

`cast` is preferrable over `# type: ignore` as it gives more information. `assert` should only be used in rare cases.

Uncertainties:

* `ByteStringObject` vs `TextStringObject`, e.g. for `_authenticateUserPassword` and the functions in `_security`
* `ContentStream`: I have no clue what type the stream argument should have

Details:

* utils.ConvertFunctionsToVirtualList -> _VirtualList 
* Typeguard was used to verify that the annotated types are correct. There are
  still some cases where Typeguard fails, but the reason might be that
  Typeguard does not consider inheritance.
* BUG: Potential None attribute access in _reader.getDestinationPageNumber
* BUG: _security._alg33_1 : Adding str and bytes argument
* STY: Fix typo 'test_get_destination_age_number'
* BUG: Field.additionalActions was missing a return statement

Signed-off-by: Matthew Peveler <matt.peveler@gmail.com>

See #863

Co-authored-by: Martin Thoma <info@martin-thoma.de>

This is important for some PyPDF2 developers development workflows.
It allows them to compare changes more easily.

Additionally, some imports were moved from function-level to module-level.

See #865 (comment)

Co-authored-by: pubpub-zz <4083478+pubpub-zz@users.noreply.github.com>

This allows us to have a simpler user interface for page transformations

Add stacklevel=2 to deprecation warnings

This is `git merge main -s ours`