ci: Use python to extract JS snippets from style guide

The job that lints code snippets in the style guide only runs
when either the documentation or the linting rules are changed.

Because of that it went unnoticed that the awk tool it uses to
extract the snippets is no longer available since the CI image
was rebased to F42.

Given that awk is awkward anyway, use the opportunity to rewrite the
snippet extraction in python instead of adding awk back to the image.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3694>

.gitlab-ci/eslint-coding-style.sh

@@ -6,36 +6,36 @@ trap "rm -rf $OUTDIR" EXIT
 
 # Turn ```javascript``` code snippets in the
 # style guide into .js files in $OUTDIR
-awk --assign dir=$OUTDIR -- '
-  BEGIN {
-    do_print = 0;
-    cur = 0;
-  }
+cat <<'EOF' | python3 - docs/js-coding-style.md $OUTDIR
+import sys
+import re
 
-  # end of code snippet
-  /```$/ {
-    do_print = 0;
-    cur++;
-  }
+def extract_js_snippets(input_file, output_dir):
+    with open(input_file, 'r') as file:
+        content = file.read()
 
-  do_print {
-    # remove one level of indent
-    sub("    ","")
+    # Find all JavaScript code blocks using regex
+    js_blocks = re.findall(r'```javascript\n(.*?)\n?```', content, flags=re.DOTALL)
 
-    # the following are class snippets, turn them
-    # into functions to not confuse eslint
-    sub("moveActor","function moveActor")
-    sub("desaturateActor","function desaturateActor")
+    for i, (match) in enumerate(js_blocks):
+        js_code = match
 
-    # finally, append to the currently generated .js file
-    print >> dir "/" cur ".js";
-  }
+        # Remove one level of indent
+        js_code = re.sub(r'^ {4}', '', js_code, flags=re.MULTILINE)
 
-  # start of code snippet
-  /```javascript$/ {
-    do_print = 1;
-  }
-' docs/js-coding-style.md
+        # The following are class snippets, turn them
+        # into functions to not confuse eslint
+        js_code = re.sub(r'^moveActor', 'function moveActor', js_code)
+        js_code = re.sub(r'^desaturateActor', 'function desaturateActor', js_code)
+
+        # Finally, create a .js file in the output directory
+        output_filename = f'{output_dir}/{i}.js'
+        with open(output_filename, 'w') as out_file:
+            out_file.write(f'{js_code}\n')
+
+input_file, output_dir = sys.argv[1:]
+extract_js_snippets(input_file, output_dir)
+EOF
 
 eslint \
   --rule 'no-undef: off' \