minor #19389 [Console] Application update PHPDoc of add and register methods (SpacePossum)

This PR was squashed before being merged into the 2.7 branch (closes #19389).

Discussion
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[Console] Application update PHPDoc of add and register methods

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

The [PHPDoc](https://github.com/symfony/symfony/blob/2.7/src/Symfony/Component/Console/Application.php#L354) states the method will always return a command, but it doesn't. Since [Application::register](https://github.com/symfony/symfony/blob/2.7/src/Symfony/Component/Console/Application.php#L328) returns the result of `add` directly is also doesn't always return the command (as its PHPDoc states).

Commits
-------

6f0474f [Console] Application update PHPDoc of add and register methods

Author: nicolas-grekas

src/Symfony/Component/Console/Application.php

@@ -213,7 +213,7 @@ public function getHelperSet()
     }
 
     /**
-     * Set an input definition set to be used with this application.
+     * Set an input definition to be used with this application.
      *
      * @param InputDefinition $definition The input definition
      */
@@ -335,6 +335,8 @@ public function register($name)
     /**
      * Adds an array of command objects.
      *
+     * If a Command is not enabled it will not be added.
+     * 
      * @param Command[] $commands An array of commands
      */
     public function addCommands(array $commands)
@@ -348,10 +350,11 @@ public function addCommands(array $commands)
      * Adds a command object.
      *
      * If a command with the same name already exists, it will be overridden.
+     * If the command is not enabled it will not be added.
      *
      * @param Command $command A Command object
      *
-     * @return Command The registered command
+     * @return Command|null The registered command if enabled or null
      */
     public function add(Command $command)
     {
@@ -420,9 +423,9 @@ public function has($name)
     /**
      * Returns an array of all unique namespaces used by currently registered commands.
      *
-     * It does not returns the global namespace which always exists.
+     * It does not return the global namespace which always exists.
      *
-     * @return array An array of namespaces
+     * @return string[] An array of namespaces
      */
     public function getNamespaces()
     {
@@ -954,7 +957,7 @@ private function getSttyColumns()
     /**
      * Runs and parses mode CON if it's available, suppressing any error output.
      *
-     * @return string <width>x<height> or null if it could not be parsed
+     * @return string|null <width>x<height> or null if it could not be parsed
      */
     private function getConsoleMode()
     {
@@ -1013,7 +1016,7 @@ public function extractNamespace($name, $limit = null)
      * @param string             $name       The string
      * @param array|\Traversable $collection The collection
      *
-     * @return array A sorted array of similar string
+     * @return string[] A sorted array of similar string
      */
     private function findAlternatives($name, $collection)
     {
@@ -1121,7 +1124,7 @@ private function splitStringByWidth($string, $width)
      *
      * @param string $name The full name of the command
      *
-     * @return array The namespaces of the command
+     * @return string[] The namespaces of the command
      */
     private function extractAllNamespaces($name)
     {