ci: Split POTFILES check between C and JS

Regex are a crude tool for analyzing whether some code *calls* a
particular function. Spidermonkey has Reflect.parse() that returns
the AST of the passed in code, which allows for a much more precise
check for javascript.

The old script is still used for C code, where i18n-affecting changes
are much rarer.

Based heavily on Philip Chimento's mozjs migration script at
https://gitlab.gnome.org/ptomato/moz60tool.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1941>

.gitlab-ci.yml

@@ -160,7 +160,7 @@ eslint_mr:
             junit: ${LINT_MR_LOG}
         when: always
 
-potfile_check:
+potfile_c_check:
     extends:
         - .fdo.distribution-image@fedora
         - .gnome-shell.fedora:34
@@ -168,6 +168,14 @@ potfile_check:
     script:
         - ./.gitlab-ci/check-potfiles.sh
 
+potfile_js_check:
+    extends:
+        - .fdo.distribution-image@fedora
+        - .gnome-shell.fedora:34
+    stage: review
+    script:
+        - js78 -m .gitlab-ci/check-potfiles.js
+
 no_template_check:
     extends:
         - .fdo.distribution-image@fedora