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/host-process.h

@@ -18,8 +18,8 @@
 
 #include <thread>
 
-#include <boost/asio/local/stream_protocol.hpp>
-#include <boost/asio/streambuf.hpp>
+#include <asio/local/stream_protocol.hpp>
+#include <asio/streambuf.hpp>
 #include <boost/process/child.hpp>
 #include <boost/process/extend.hpp>
 #include <boost/process/io.hpp>
@@ -91,8 +91,11 @@ class HostProcess {
             // FIXME: Replace Boost.Filesystem
             host_path.string(),
 #endif  // WITH_WINEDBG
-            boost::process::std_out = stdout_pipe_,
-            boost::process::std_err = stderr_pipe_,
+        // FIXME: This won't work with our patched async_pipe version
+        // boost::process::std_out = stdout_pipe_,
+        // boost::process::std_err = stderr_pipe_,
+            patched_async_pipe_out<1, -1>(stdout_pipe_),
+            patched_async_pipe_out<2, -1>(stderr_pipe_),
             // NOTE: If the Wine process outlives the host, then it may cause
             //       issues if our process is still keeping the host's file
             //       descriptors alive that. This can prevent Ardour from
@@ -140,7 +143,7 @@ class HostProcess {
      *   with the plugin. When the plugin shuts down, we'll close all of the
      *   sockets used by the plugin.
      */
-    HostProcess(boost::asio::io_context& io_context,
+    HostProcess(asio::io_context& io_context,
                 Logger& logger,
                 const Configuration& config,
                 Sockets& sockets);
@@ -171,8 +174,8 @@ class HostProcess {
      */
     Logger& logger_;
 
-    boost::asio::streambuf stdout_buffer_;
-    boost::asio::streambuf stderr_buffer_;
+    asio::streambuf stdout_buffer_;
+    asio::streambuf stderr_buffer_;
 };
 
 /**
@@ -201,7 +204,7 @@ class IndividualHost : public HostProcess {
      * @throw std::runtime_error When `plugin_path` does not point to a valid
      *   32-bit or 64-bit .dll file.
      */
-    IndividualHost(boost::asio::io_context& io_context,
+    IndividualHost(asio::io_context& io_context,
                    Logger& logger,
                    const Configuration& config,
                    Sockets& sockets,
@@ -249,7 +252,7 @@ class GroupHost : public HostProcess {
      * @param host_request The information about the plugin we should launch a
      *   host process for. This object will be sent to the group host process.
      */
-    GroupHost(boost::asio::io_context& io_context,
+    GroupHost(asio::io_context& io_context,
               Logger& logger,
               const Configuration& config,
               Sockets& sockets,