💥 Rename HostBridge to PluginBridge

As mentioned in the last commit. The original reasoning behind these
names was that the HostBridge talks to the host, and the PluginBridge
talks to the plugin, but you could also argue that the HostBridge should
be part of the Wine VST host and the PluginBridge should be part of the
VST plugin. This removes that ambiguity.

meson.build

@@ -60,8 +60,8 @@ shared_library(
   [
     'src/common/logging.cpp',
     'src/common/serialization.cpp',
-    'src/plugin/host-bridge.cpp',
     'src/plugin/plugin.cpp',
+    'src/plugin/plugin-bridge.cpp',
     version_header,
   ],
   native : true,