feature #36775 [DependencyInjection] Add abstract_arg() and param() (fabpot)

This PR was squashed before being merged into the 5.2-dev branch.

Discussion
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[DependencyInjection] Add abstract_arg() and param()

| Q             | A
| ------------- | ---
| Branch?       | maste
| Bug fix?      | no
| New feature?  | yes <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | n/a <!-- prefix each issue number with "Fix #", if any -->
| License       | MIT
| Doc PR        | -

Added abstract_arg() and param() to configuration abstract arguments in PHP DSL.

Commits
-------

1fd4e8bb60 [DependencyInjection] Add abstract_arg() and param()

src/Symfony/Component/DependencyInjection/Loader/Configurator/AbstractConfigurator.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\DependencyInjection\Loader\Configurator;
 
+use Symfony\Component\DependencyInjection\Argument\AbstractArgument;
 use Symfony\Component\DependencyInjection\Argument\ArgumentInterface;
 use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Exception\InvalidArgumentException;
@@ -85,6 +86,7 @@ abstract class AbstractConfigurator
             case $value instanceof Definition:
             case $value instanceof Expression:
             case $value instanceof Parameter:
+            case $value instanceof AbstractArgument:
             case $value instanceof Reference:
                 if ($allowServices) {
                     return $value;

src/Symfony/Component/DependencyInjection/Loader/Configurator/ContainerConfigurator.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\DependencyInjection\Loader\Configurator;
 
+use Symfony\Component\DependencyInjection\Argument\AbstractArgument;
 use Symfony\Component\DependencyInjection\Argument\IteratorArgument;
 use Symfony\Component\DependencyInjection\Argument\ServiceLocatorArgument;
 use Symfony\Component\DependencyInjection\Argument\TaggedIteratorArgument;
@@ -82,6 +83,14 @@ class ContainerConfigurator extends AbstractConfigurator
     }
 }
 
+/**
+ * Creates a parameter.
+ */
+function param(string $name): string
+{
+    return '%'.$name.'%';
+}
+
 /**
  * Creates a service reference.
  *
@@ -165,3 +174,11 @@ function expr(string $expression): Expression
 {
     return new Expression($expression);
 }
+
+/**
+ * Creates an abstract argument.
+ */
+function abstract_arg(string $description): AbstractArgument
+{
+    return new AbstractArgument($description);
+}