Replace Boost.Asio with standalone Asio library

We had to add an even hackier hack now to get Boost.Process to
interoperate with Asio's IO contexts. This will be replaced later when
we replace Boost.Process.

src/plugin/bridges/common.h

@@ -74,7 +74,7 @@ class PluginBridge {
      *   found, or if it could not locate and load a VST3 module.
      */
     template <invocable_returning<TSockets,
-                                  boost::asio::io_context&,
+                                  asio::io_context&,
                                   const PluginInfo&> F>
     PluginBridge(PluginType plugin_type, F&& create_socket_instance)
         // This is still correct for VST3 plugins because we can configure an
@@ -367,7 +367,7 @@ class PluginBridge {
         // sockets and we'll be hanging here indefinitely. To prevent this,
         // we'll periodically poll whether the Wine process is still running,
         // and throw when it is not. The alternative would be to rewrite this to
-        // using `async_accept`, Boost.Asio timers, and another IO context, but
+        // using `async_accept`, Asio timers, and another IO context, but
         // I feel like this a much simpler solution.
         host_watchdog_handler_ = std::jthread([&](std::stop_token st) {
             using namespace std::literals::chrono_literals;
@@ -441,7 +441,7 @@ class PluginBridge {
      */
     const PluginInfo info_;
 
-    boost::asio::io_context io_context_;
+    asio::io_context io_context_;
 
     /**
      * The sockets used for communication with the Wine process.
@@ -485,7 +485,7 @@ class PluginBridge {
     std::future<bool> has_realtime_priority_;
 
     /**
-     * Runs the Boost.Asio `io_context_` thread for logging the Wine process
+     * Runs the Asio `io_context_` thread for logging the Wine process
      * STDOUT and STDERR messages.
      */
     std::jthread wine_io_handler_;