feature #40059 [PhpUnitBridge] Add SYMFONY_PHPUNIT_REQUIRE env variable (acasademont)

This PR was merged into the 5.3-dev branch.

Discussion
----------

[PhpUnitBridge] Add SYMFONY_PHPUNIT_REQUIRE env variable

| Q             | A
| ------------- | ---
| Branch?       | 5.x
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | Fix #39387
| License       | MIT
| Doc PR        | symfony/symfony-docs#14913

As discussed on #39387, this PR adds a new `SYMFONY_PHPUNIT_REQUIRE` env variable to add packages to the phpunit bridge installation. This is useful for adding phpunit plugins (ie: https://github.com/phpspec/prophecy-phpunit) without having to add them directly to the main app composer.json.

On my `phpunit.xml.dist` file I can now add

```xml
<server name="SYMFONY_PHPUNIT_REQUIRE" value="phpspec/prophecy-phpunit"/>
```

And the `phpspec/prophecy-phpunit` will be installed along the rest of the phpunit packages

Commits
-------

94e1d877eb Add SYMFONY_PHPUNIT_REQUIRE env variable Fixes #39387

Author: fabpot

bin/simple-phpunit.php

@@ -167,7 +167,8 @@
     }
 }
 $SYMFONY_PHPUNIT_REMOVE = $getEnvVar('SYMFONY_PHPUNIT_REMOVE', 'phpspec/prophecy'.($PHPUNIT_VERSION < 6.0 ? ' symfony/yaml' : ''));
-$configurationHash = md5(implode(\PHP_EOL, [md5_file(__FILE__), $SYMFONY_PHPUNIT_REMOVE, (int) $PHPUNIT_REMOVE_RETURN_TYPEHINT]));
+$SYMFONY_PHPUNIT_REQUIRE = $getEnvVar('SYMFONY_PHPUNIT_REQUIRE', '');
+$configurationHash = md5(implode(\PHP_EOL, [md5_file(__FILE__), $SYMFONY_PHPUNIT_REMOVE, $SYMFONY_PHPUNIT_REQUIRE, (int) $PHPUNIT_REMOVE_RETURN_TYPEHINT]));
 $PHPUNIT_VERSION_DIR = sprintf('phpunit-%s-%d', $PHPUNIT_VERSION, $PHPUNIT_REMOVE_RETURN_TYPEHINT);
 if (!file_exists("$PHPUNIT_DIR/$PHPUNIT_VERSION_DIR/phpunit") || $configurationHash !== @file_get_contents("$PHPUNIT_DIR/.$PHPUNIT_VERSION_DIR.md5")) {
     // Build a standalone phpunit without symfony/yaml nor prophecy by default
@@ -224,6 +225,9 @@
     if ($SYMFONY_PHPUNIT_REMOVE) {
         $passthruOrFail("$COMPOSER remove --no-update ".$SYMFONY_PHPUNIT_REMOVE);
     }
+    if ($SYMFONY_PHPUNIT_REQUIRE) {
+        $passthruOrFail("$COMPOSER require --no-update ".$SYMFONY_PHPUNIT_REQUIRE);
+    }
     if (5.1 <= $PHPUNIT_VERSION && $PHPUNIT_VERSION < 5.4) {
         $passthruOrFail("$COMPOSER require --no-update phpunit/phpunit-mock-objects \"~3.1.0\"");
     }