Kernel+LibELF+LibCoreDump+CrashReporter: Use JSON for ProcessInfo

This is in preparation of adding (much) more process information to
coredumps. As we can only have one null-terminated char[] of arbitrary
length in each struct it's now a single JSON blob, which is a great fit:
easily extensible in the future and allows for key/value pairs and even
nested objects, which will be used e.g. for the process environment, for
example.

Userland/Libraries/LibCoreDump/Reader.h

@@ -44,8 +44,6 @@ public:
     static OwnPtr<Reader> create(const String&);
     ~Reader();
 
-    const ELF::Core::ProcessInfo& process_info() const;
-
     template<typename Func>
     void for_each_memory_region_info(Func func) const;
 
@@ -66,6 +64,10 @@ public:
     const LibraryData* library_containing(FlatPtr address) const;
 
     const Backtrace backtrace() const;
+
+    int process_pid() const;
+    u8 process_termination_signal() const;
+    String process_executable_path() const;
     const HashMap<String, String> metadata() const;
 
 private:
@@ -86,6 +88,11 @@ private:
         const u8* start { nullptr };
     };
 
+    // Private as we don't need anyone poking around in this JsonObject
+    // manually - we know very well what should be included and expose that
+    // as getters with the appropriate (non-JsonValue) types.
+    const JsonObject process_info() const;
+
     NonnullRefPtr<MappedFile> m_coredump_file;
     ELF::Image m_coredump_image;
     ssize_t m_notes_segment_index { -1 };