Interpolate named counts in JS

Even though JS does the `%d` interpolation in `n__` using a string
replacement. This would not be compatible with the ruby
implementation.

Therefore using named variables instead.

app/assets/javascripts/ide/components/commit_sidebar/list_collapsed.vue

@@ -38,14 +38,17 @@ export default {
       return this.modifiedFilesLength ? 'multi-file-modified' : '';
     },
     additionsTooltip() {
-      return sprintf(n__('1 %{type} addition', '%d %{type} additions', this.addedFilesLength), {
+      return sprintf(n__('1 %{type} addition', '%{count} %{type} additions', this.addedFilesLength), {
         type: this.title.toLowerCase(),
+        count: this.addedFilesLength,
       });
     },
     modifiedTooltip() {
       return sprintf(
-        n__('1 %{type} modification', '%d %{type} modifications', this.modifiedFilesLength),
-        { type: this.title.toLowerCase() },
+        n__('1 %{type} modification', '%{count} %{type} modifications', this.modifiedFilesLength), {
+          type: this.title.toLowerCase(),
+          count: this.modifiedFilesLength,
+        },
       );
     },
     titleTooltip() {