This is a big simplification of all IntrusiveHashSet users: instead of
having to implement multiple overloads of Hash and Equal, the
IntrusiveHashSet class can first extract the effective key from an
item and then pass it to the Hash/Equal functions.
Preparing to add a key extraction function. Without this "Operators"
template parameter, we'd have even more template parameters, and that
parameter list would grow too complex. Better wrap it in one single
template that contains all operators.
This is an API change which all callers need to adjust to, but it will
be worth it.
Fix build with Boost 1.81.0. `<array>` was included by one of those boost headers,
however, it's no longer included as of Boost 1.81.0.
`master` doesn't use `std::array` in this file.
While we're at it, add all necessary inclusion files.
Since we switched from autotools to Meson in commit
94592c1406, we don't need to include
`config.h` early to properly enable large file support. Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.
This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.
