[Clang-Tidy] New check `bugprone-redundant-branch-condition`

Checking the same condition again in a nested `if` usually make no sense,
except if the value of the expression could have been changed between
the two checks. Although compilers may optimize this out, such code is
suspicious: the programmer may have meant to check something else.
Therefore it is worth to find such places in the code and notify the
user about the problem.

This patch implements a basic check for this problem. Currently it
only detects redundant conditions where the condition is a variable of
integral type. It also detects the possible bug if the variable is in an
//or// or //and// logical expression in the inner if and/or the variable
is in an //and// logical expression in the outer if statement. Negated
cases are not handled yet.

Differential Revision: https://reviews.llvm.org/D81272