[bug] expose `conan.tools.files.sha256sum`

[SSE4]

Environment details

• Operating System+version: Linux debian 6.1.8-x64v3-custom-xanmod1 #1 SMP PREEMPT_DYNAMIC Tue Jan 31 19:37:53 +07 2023 x86_64 GNU/Linux
• Compiler+version: g++ (GCC) 12.2.0
• Conan version: Conan version 2.0.0-beta9
• Python version: Python 3.9.2

Steps to reproduce

1. python -c "from conan.tools.files import sha256sum"

Logs

Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: cannot import name 'sha256sum' from 'conan.tools.files' (/home/sse4/.local/lib/python3.9/site-packages/conan/tools/files/__init__.py)

[uilianries]

We have only one case in ConanCenterIndex which uses it, the ICU recipe. I really don't know if worth porting it, it's a simple feature, but the chorus is too small.

[SSE4]

besides conan center, there are billions of private (enterprise) recipes that we don't see. it's simple thing, so exposing it is not a big deal (especially given it's already implemented in the code).