touch: inject touches from spiceapi to native touch hooks (#824)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #814

## Description of change
Touches via the API wasn't being delivered to native touch hook;
implement this, which closes the last gap we have vs. wintouchemu.

While we're here, implement popn subscreen support for companion as
well.

## Testing
Tested for iidx/sdvx/popn

src/spice2x/touch/native/inject.h

@@ -9,5 +9,6 @@ namespace nativetouch::inject {
     void register_and_attach_window(HWND window);
     void hook(HMODULE module);
     bool inject_synthetic_touch(POINT position, bool down);
+    bool inject_synthetic_touch_from_canvas(POINT position, SIZE canvas, bool down);
     bool transform_touch_input(tagTOUCHINPUT *point);
 }