refactor: replace boost::filesystem with std::filesystem

Warning: Replacing fs::system_complete calls with fs::absolute calls
in this commit may cause minor changes in behaviour because fs::absolute
no longer strips trailing slashes; however these changes are believed to
be safe.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

src/init.cpp

@@ -72,10 +72,13 @@
 #include <validationinterface.h>
 #include <walletinitinterface.h>
 
+#include <condition_variable>
+#include <cstdint>
+#include <cstdio>
+#include <fstream>
 #include <functional>
 #include <set>
-#include <stdint.h>
-#include <stdio.h>
+#include <string>
 #include <thread>
 #include <vector>
 
@@ -137,7 +140,7 @@ static fs::path GetPidFile(const ArgsManager& args)
 
 [[nodiscard]] static bool CreatePidFile(const ArgsManager& args)
 {
-    fsbridge::ofstream file{GetPidFile(args)};
+    std::ofstream file{GetPidFile(args)};
     if (file) {
 #ifdef WIN32
         tfm::format(file, "%d\n", GetCurrentProcessId());