Don't delete default constructor of PathDiagnosticConsumerOptions

This type is used as an aggregate, i.e. it has no member functions.
Starting with C++20 types with deleted default constructors are not
aggregate types anymore which means that aggregate initialization will
not work for this class anymore. This leads to a compile error in
clang::AnalyzerOptions::getDiagOpts() for example.

Also set the boolean flags to false by default to avoid undefined
behavior. Previously this was prevented by deleting the default
constructor, now we explicitly initialize them.

Differential Revision: https://reviews.llvm.org/D92221