Rename library targets and update to PEGTL 3.2.0

The naming of graphqlservice_nointrospection vs. graphqlservice was confusing, although it did mean that CMake builds which linked against graphqlservice kept working without modification. It is still source compatible, but I decided to break backwards compatibility with CMake builds by renaming graphqlservice_nointrospection back to graphqlservice, and graphqlservice (which depends on that and just adds Introspection support) to graphqlintrospection.

If you use CMake and you want to include Introspection support, add cppgraphqlgen::graphqlintrospection to your target_link_libraries. You can also just replace cppgraphqlgen::graphqlservice with that, it exports a public link dependency on graphqlservice. If you do not use CMake in your own project, but you still built/installed cppgraphqlgen using CMake (including using a package manager like vcpkg), then you need to link against both target libraries.

If you do not want Introspection support, you can regenerate your schema implementation with schemagen --no-introspection, and instead of linking against graphqlintrospection, just link against graphqlservice.

PEGTL released 3.2.0 which includes the fix for the demangle namespace, so cppgraphqlgen no longer depends on a pre-release version of PEGTL or a preprocessor workaround to redeclare demangle in the expected namespace with 3.1.0.