Symfony version(s) affected: 5.1.8

Description
Symfony\Component\Intl\Locale::getFallback() throws an ErrorException when the length of specified $locale is greater than INTL_MAX_LOCALE_LEN.

How to reproduce

Locale::getFallback("LC_CTYPE=fr_FR.UTF-8;LC_NUMERIC=C;LC_TIME=fr_FR.UTF-8;LC_COLLATE=fr_FR.UTF-8;LC_MONETARY=fr_FR.UTF-8;LC_MESSAGES=fr_FR.UTF-8;LC_PAPER=fr_FR.UTF-8;LC_NAME=fr_FR.UTF-8;LC_ADDRESS=fr_FR.UTF-8;LC_TELEPHONE=fr_FR.UTF-8;LC_MEASUREMENT=fr_FR.UTF-8;LC_IDENTIFICATION=fr_FR.UTF-8");
// Uncaught ErrorException: count(): Parameter must be an array or an object that implements Countable in /home/www/grossiste/vendor/symfony/intl/Locale.php:70

Possible Solution
locale_parse() returns null instead of an array when the specified locale is greater than INTL_MAX_LOCALE_LEN. So a check should be made to test whether the return value is an array. Or, the locale could be shortened by only extracting the meaningful part (i.e. just keep LC_MESSAGES=fr_FR.UTF-8?).

Additional context
Length of the system locale: 270 (i.e. the one in the given code sample).
Value of the INTL_MAX_LOCALE_LEN constant: 156.

PHP: 7.4.9 (x64) on CentOS 7.
Intl extension:

• Internationalization support => enabled
• ICU version => 65.1
• ICU Data version => 65.1
• ICU TZData version => 2019c
• ICU Unicode version => 12.1