[clang-tidy] Update bugprone-stringview-nullptr to consistently prefer the...

[clang-tidy] Update bugprone-stringview-nullptr to consistently prefer the empty string when passing arguments to constructors/functions

Previously, function(nullptr) would have been fixed with function({}). This unfortunately can change overload resolution and even become ambiguous. T(nullptr) was already being fixed with T(""), so this change just brings function calls in line with that.

Differential Revision: https://reviews.llvm.org/D117840