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.

meson.build

@@ -46,7 +46,7 @@ compiler_options = [
   '-fvisibility-inlines-hidden',
   # Disable the use of concepts in Boost.Asio until Boost 1.73 gets released
   # https://github.com/boostorg/asio/issues/312
-  # TODO: Rename after switching to non-Boost ASIO
+  # TODO: Rename after switching out Boost.Process
   '-DBOOST_ASIO_DISABLE_CONCEPTS',
   # Boost.Process's auto detection for vfork() support doesn't seem to work
   # TODO: Remove after adding our own library
@@ -232,6 +232,7 @@ endif
 # These are all headers-only libraries, and thus won't require separate 32-bit
 # and 64-bit versions
 
+asio_dep = dependency('asio', version : '>=1.22.0')
 boost_dep = dependency('boost', version : '>=1.66', static : with_static_boost)
 if meson.version().version_compare('>=0.60')
   # Bitsery's CMake build definition is capitalized for some reason
@@ -295,6 +296,7 @@ shared_library(
   dependencies : [
     configuration_dep,
 
+    asio_dep,
     boost_dep,
     with_32bit_libraries
       ? boost_filesystem_32bit_dep
@@ -320,6 +322,7 @@ if with_vst3
     dependencies : [
       configuration_dep,
 
+      asio_dep,
       boost_dep,
       with_32bit_libraries
         ? boost_filesystem_32bit_dep