Bug 1766045 - Adding mach command to generate UniFFI files r=glandium

Added `mach uniffi generate` which executes `uniffi-bindgen-gecko-js` to
generate UniFFI bindings. It's unfortunate that we need to check these
files in, but I couldn't figure out a way to auto-generate them as part
of the build process.

Adding `#include "nsIContent.h"` to dom/base/nsINodeList.h.  I think
that should have been present before, but things built okay because of
the way things got combined in the uniffied .cpp files. Adding these new
webIDL files bumped `NodeListBinding.cpp` to a new uniffied .cpp file
which caused the build to fail.

Differential Revision: https://phabricator.services.mozilla.com/D144468

build/mach_initialize.py

@@ -363,6 +363,9 @@ def initialize(topsrcdir):
         ),
         "esmify": MachCommandReference("tools/esmify/mach_commands.py"),
         "xpcshell": MachCommandReference("js/xpconnect/mach_commands.py"),
+        "uniffi": MachCommandReference(
+            "toolkit/components/uniffi-bindgen-gecko-js/mach_commands.py"
+        ),
     }
 
     # Set a reasonable limit to the number of open files.