Allow formatPlural's plural string not to have '@count' in it in JavaScript

The current regex used in _locale_parse_js_file (file core/modules/locale/locale.module) doesn't allow to format plural string that doesn't contains @count in it.

The current regex looks like this:

'~
    [^\w]Drupal\s*\.\s*formatPlural\s*  # match "Drupal.formatPlural" with whitespace
    \(                                  # match "(" argument list start
    \s*.+?\s*,\s*                       # match count argument
    (' . LOCALE_JS_STRING . ')\s*,\s*   # match singular string argument
    (                             # capture plural string argument
      (?:                         # non-capturing group to repeat string pieces
        (?:
          \'                      # match start of single-quoted string
          (?:\\\\\'|[^\'])*       # match any character except unescaped single-quote
          @count                  # match "@count"
          (?:\\\\\'|[^\'])*       # match any character except unescaped single-quote
          \'                      # match end of single-quoted string
          |
          "                       # match start of double-quoted string
          (?:\\\\"|[^"])*         # match any character except unescaped double-quote
          @count                  # match "@count"
          (?:\\\\"|[^"])*         # match any character except unescaped double-quote
          "                       # match end of double-quoted string
        )
        (?:\s*\+\s*)?             # match "+" with possible whitespace, for str concat
      )+                          # match multiple because we supports concatenating strs
    )\s*                          # end capturing of plural string argument
    (?:,\s*' . LOCALE_JS_OBJECT . '\s*          # optionally capture string args
      (?:,\s*' . LOCALE_JS_OBJECT_CONTEXT . '\s*)?  # optionally capture context
    )?
    [,\)]
    ~sx';

With this regex, this JavaScript code will be correctly matched and translations will be available:

Drupal.formatPlural(quantity, "element", "@count elements");

But this JavaScript code will not be matched and translations will not be available:

Drupal.formatPlural(quantity, "element", "elements");

Proposed resolution: avoid having to have @count in the plural argument by modifying the regex like this:

'~
    [^\w]Drupal\s*\.\s*formatPlural\s*  # match "Drupal.formatPlural" with whitespace
    \(                                  # match "(" argument list start
    \s*.+?\s*,\s*                       # match count argument
    (' . LOCALE_JS_STRING . ')\s*,\s*   # match singular string argument
    (                             # capture plural string argument
      (?:                         # non-capturing group to repeat string pieces
        (?:
          \'(?:\\\\\'|[^\'])*\'   # match single-quoted string
          |
          "(?:\\\\"|[^"])*"  # match double-quoted string
        )
        (?:\s*\+\s*)?             # match "+" with possible whitespace, for str concat
      )+                          # match multiple because we supports concatenating strs
    )\s*                          # end capturing of plural string argument
    (?:,\s*' . LOCALE_JS_OBJECT . '\s*          # optionally capture string args
      (?:,\s*' . LOCALE_JS_OBJECT_CONTEXT . '\s*)?  # optionally capture context
    )?
    [,\)]
    ~sx';