Auto merge of #29600 - mrobinson:layout-2020-args, r=jdm

Have all mach command accept "--with-layout-2020" and "--layout-2020"

Some command accepted one and some the other. This changes makes them all accept both so it's no longer necessary to remember which uses which.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they change the arguments accepted by mach.

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tests/wpt/update/updatecommandline.py

@@ -13,7 +13,7 @@ def create_parser():
     parser.add_argument("--token-file", action="store", type=wptcommandline.abs_path,
                         help="Path to file containing github token")
     parser.add_argument("--token", action="store", help="GitHub token to use")
-    parser.add_argument('--layout-2020', default=False, action="store_true",
+    parser.add_argument("--layout-2020", "--with-layout-2020", default=False, action="store_true",
                         help="Use expected results for the 2020 layout engine")
     return parser