byte: workaround for c++17 std::byte definition

[d-a-v]

This patch renames the Arduino type byte to something else in order to avoid ambiguous/conflicting types when c++17, byte, and using namespace std are used together.
This follows up #8089 (comment), gmag11/NtpClient#115 and things4u/ESP-1ch-Gateway#82.

This comment is true but libraries and projects will prefer to use previous version of this core than to fix.
In the Arduino world, ascendant compatibility still prevails.

This is a hack, relying on the following facts

• Arduino byte is always defined in Arduino.h
• std::byte is declared only in <cstddef> <functional> and <bits/cpp_type_traits.h>.
  The two latters were found with grep after noticing that the first was not sufficient.

fixes #8089