QModBusPdu: replace deprecated std::is_trivial with its definition

ie. is_trivially_copyable && is_trivially_default_constructible

C++26 deprecates std::is_trivial. The replacements have been available
since C++11.

As a drive-by, port from raw && to std::conjunction.

Amends 275ed191e6452d7e623cff0cde0beb9e416a8e46.

Pick-to: 6.11 6.10 6.8 6.5
Change-Id: I2c302dd65783ee90c1b5b15ce4c6c554e416012b
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>