build: do not depend on cp in PATH

Use gyp’s own copying mechanism instead.

It’s not really clear which UNIX utils exactly are needed to build on
Windows, but this is an easier fix (at least for me) than figuring
out how to get `cp` into the `PATH` in all cases, and judging
from the issue I’m not the only one who ran into this.

Fixes: nodejs#20272

node.gyp

@@ -680,13 +680,13 @@
       'toolsets': ['host'],
       'conditions': [
         [ 'v8_enable_inspector==1', {
-          'actions': [
+          'copies': [
             {
-              'action_name': 'v8_inspector_copy_protocol_to_intermediate_folder',
-              'inputs': [ 'deps/v8/src/inspector/js_protocol.pdl' ],
-              'outputs': [ '<(SHARED_INTERMEDIATE_DIR)/js_protocol.pdl' ],
-              'action': [ 'cp', '<@(_inputs)', '<(SHARED_INTERMEDIATE_DIR)' ],
-            },
+              'destination': '<(SHARED_INTERMEDIATE_DIR)',
+              'files': ['deps/v8/src/inspector/js_protocol.pdl']
+            }
+          ],
+          'actions': [
             {
               'action_name': 'v8_inspector_convert_protocol_to_json',
               'inputs': [