Merge pull request swiftlang#5657 from gottesmm/add_syntax_highlighting_for_openexistentialmetatype

[sil-mode] Add syntax highlighting for open_existential_metatype.

Author: gottesmm

utils/sil-mode.el

@@ -120,6 +120,7 @@
                     "open_existential_addr" "alloc_existential_box"
                     "init_existential_ref" "project_existential_box"
                     "open_existential_ref" "open_existential_box"
+                    "open_existential_metatype"
                     "objc_protocol")
                   'words) . font-lock-keyword-face)
    ;; Unchecked Conversions