rawinput: avoid deadlock when binding analog axis as a button (#809)

## Link to GitHub Issue or related Pull Request, if one exists
Regressed by #793

## Description of change
Due to lock inversion, when binding an analog axis as a button, spice
deadlocks. Fix that.

Also create a separate `unordered_map` that keeps track of device
handles so that `WM_INPUT` handle can look up devices without having to
acquire the larger `devices_mutex` which could be held by (potentially)
lengthy operations like hotplug.

Fix more synchronization issues around hotplug. Latent bug exposed by
MIDI 2.0 issues.

## Testing

src/spice2x/rawinput/midi.cpp

@@ -238,8 +238,6 @@ void rawinput::RawInputManager::devices_scan_midi() {
         midi_device.name = midi_identifier;
         midi_device.desc = to_string(midi_device_caps.szPname);
         midi_device.info = midi_device_info;
-        midi_device.mutex = new std::mutex();
-        midi_device.mutex_out = new std::mutex();
         midi_device.midiInfo = midi_device_midi_info;
 
         // mutate the shared device list under lock (the slow WinMM calls above
@@ -256,10 +254,9 @@ void rawinput::RawInputManager::devices_scan_midi() {
                 // carry over ID
                 midi_device.id = device.id;
 
-                // destruct and replace, reusing the slot's existing mutexes
+                // destruct and replace the slot in place under its locks
                 this->devices_destruct(&device);
-                reuse_device_mutexes(midi_device, device);
-                device = midi_device;
+                replace_device_slot(device, midi_device);
 
                 // notify change
                 for (auto &cb : this->callback_change) {
@@ -275,6 +272,8 @@ void rawinput::RawInputManager::devices_scan_midi() {
         }
 
         // add device to list
+        midi_device.mutex = new std::mutex();
+        midi_device.mutex_out = new std::mutex();
         auto &device = this->devices.emplace_back(midi_device);
 
         // notify add