Bug 1657401 - Prelude: rearrange IPDL files in widget/. r=spohl

The IPDL compiler searches for files in an include path made up of every
directory with any `IPDL_SOURCES` in it, which means that distinct files
shouldn't have the same name or, failing that, need to be set up so they
won't accidentally conflict.  See bug 1657712 for details.

In `widget/`, the PCompositorWidget and PlatformWidgetTypes files are
overridden on some OSes; this patch moves the general-case versions into
their own directory, so that it's possible to use the widget/ toplevel
directory for non-platform-specific IPDL without causing a filename
conflict.

Differential Revision: https://phabricator.services.mozilla.com/D94530

widget/moz.build

@@ -338,9 +338,9 @@ elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk" and CONFIG["MOZ_X11"]:
     ]
 else:
     IPDL_SOURCES = [
+        "generic/PCompositorWidget.ipdl",
+        "generic/PlatformWidgetTypes.ipdlh",
         "headless/HeadlessWidgetTypes.ipdlh",
-        "PCompositorWidget.ipdl",
-        "PlatformWidgetTypes.ipdlh",
     ]
 
 LOCAL_INCLUDES += [