[clang-tidy] New check cppcoreguidelines-prefer-member-initializer

Finds member initializations in the constructor body which can be placed
into the initialization list instead. This does not only improves the
readability of the code but also affects positively its performance.
Class-member assignments inside a control statement or following the
first control statement are ignored.

Differential Revision: https://reviews.llvm.org/D71199