Replace most uses of Boost.{Filesystem,Process}

With the `ghc::filesystem` dependency from the previous commit. If we
can replace the rest of the Boost.Filesystem dependency then we can get
rid the one nasty runtime dependency we have, and it will make
implementing the chainloading simpler since can reuse more code without
bringing in Boost.

src/wine-host/bridges/group.cpp

@@ -19,7 +19,6 @@
 #include "../boost-fix.h"
 
 #include <unistd.h>
-#include <boost/process/environment.hpp>
 #include <regex>
 
 #include "../../common/communication/common.h"
@@ -30,7 +29,7 @@
 
 // FIXME: `std::filesystem` is broken in wineg++, at least under Wine 5.8. Any
 //        path operation will thrown an encoding related error
-namespace fs = boost::filesystem;
+namespace fs = ghc::filesystem;
 
 using namespace std::literals::chrono_literals;
 
@@ -86,7 +85,7 @@ StdIoCapture::~StdIoCapture() noexcept {
     close(pipe_fd_[0]);
 }
 
-GroupBridge::GroupBridge(boost::filesystem::path group_socket_path)
+GroupBridge::GroupBridge(ghc::filesystem::path group_socket_path)
     : logger_(Logger::create_from_environment(
           create_logger_prefix(group_socket_path))),
       main_context_(),
@@ -191,7 +190,7 @@ void GroupBridge::accept_requests() {
             // this process to crash during its initialization to prevent
             // waiting indefinitely on the sockets to be connected to.
             const auto request = read_object<HostRequest>(socket);
-            write_object(socket, HostResponse{boost::this_process::get_id()});
+            write_object(socket, HostResponse{.pid = getpid()});
 
             // The plugin has to be initiated on the IO context's thread because
             // this has to be done on the same thread that's handling messages,