Rename `codecs._Encoder`, `codecs._Decoder`, `.encode` and `.decode` `input` argument

[denballakh]

input argument of .encode and .decode methods shadows built-in function input, which might trigger linter checks and make code editor highlight this variable as built-in.

This shows that nobody is calling these methods using input keyword argument:
https://grep.app/search?q=decode%28input%3D&filter[lang][0]=Python
https://grep.app/search?q=encode%28input%3D&filter[lang][0]=Python

[srittau]

I haven't investigated this, but we should probably just turn them into positional-only arguments.

[sobolevn]

Yes, they are pos-only in CPython:

>>> import codecs
>>> codecs.getencoder('utf8')
<built-in function utf_8_encode>

_codecs.utf_8_encode
    str: unicode
    errors: str(accept={str, NoneType}) = None
    /

Also, docs do not specify the signature https://docs.python.org/3/library/codecs.html#codecs.getencoder

So, pos-only is our best bet.