Enable "plain function as helpers" polyfill

This feature landed in Ember 4.5+, but this polyfill would allow
it to work on 3.25+

References

RFC: emberjs/rfcs#756
Update: emberjs/rfcs#788
Guides: ember-learn/guides-source#1924

app/assets/javascripts/discourse/package.json

@@ -100,6 +100,7 @@
     "ember-cli-progress-ci": "1.0.0",
     "ember-cli-sri": "^2.1.1",
     "ember-cli-terser": "^4.0.2",
+    "ember-functions-as-helper-polyfill": "^2.1.1",
     "ember-qunit": "^6.2.0",
     "ember-exam": "^8.0.0",
     "eslint": "^8.42.0",

app/assets/javascripts/yarn.lock

@@ -4284,6 +4284,15 @@ ember-export-application-global@^2.0.1:
   resolved "https://registry.yarnpkg.com/ember-export-application-global/-/ember-export-application-global-2.0.1.tgz#b120a70e322ab208defc9e2daebe8d0dfc2dcd46"
   integrity sha512-B7wiurPgsxsSGzJuPFkpBWnaeuCu2PGpG2BjyrfA1VcL7//o+5RSnZqiCEY326y7qmxb2GoCgo0ft03KBU0rRw==
 
+ember-functions-as-helper-polyfill@^2.1.1:
+  version "2.1.1"
+  resolved "https://registry.yarnpkg.com/ember-functions-as-helper-polyfill/-/ember-functions-as-helper-polyfill-2.1.1.tgz#25240db29b4cd0366a2d2954d2ea26ce0872ff8f"
+  integrity sha512-vZ2w9G/foohwtPm99Jos1m6bhlXyyyiJ4vhLbxyjWB4wh7bcpRzXPgCewDRrwefZQ2BwtHg3c9zvVMlI0g+o2Q==
+  dependencies:
+    ember-cli-babel "^7.26.11"
+    ember-cli-typescript "^5.0.0"
+    ember-cli-version-checker "^5.1.2"
+
 ember-load-initializers@^2.1.1:
   version "2.1.2"
   resolved "https://registry.yarnpkg.com/ember-load-initializers/-/ember-load-initializers-2.1.2.tgz#8a47a656c1f64f9b10cecdb4e22a9d52ad9c7efa"