[TASK] Add native type declarations to OutputFormat

Also fix some type annotations.

Author: oliverklee

CHANGELOG.md

@@ -21,7 +21,7 @@ Please also have a look at our
 ### Changed
 
 - Use more native type declarations and strict mode
-  (#641, #772, #774, #778, #804, #841, #873)
+  (#641, #772, #774, #778, #804, #841, #873, #875)
 - Add visibility to all class/interface constants (#469)
 
 ### Deprecated

src/OutputFormat.php

@@ -170,11 +170,9 @@ class OutputFormat
     public function __construct() {}
 
     /**
-     * @param string $sName
-     *
-     * @return string|null
+     * @return string|int|bool|null
      */
-    public function get($sName)
+    public function get(string $sName)
     {
         $aVarPrefixes = ['a', 's', 'm', 'b', 'f', 'o', 'c', 'i'];
         foreach ($aVarPrefixes as $sPrefix) {
@@ -258,10 +256,7 @@ public function indentWithSpaces(int $numberOfSpaces = 2): self
         return $this->setIndentation(\str_repeat(' ', $numberOfSpaces));
     }
 
-    /**
-     * @return OutputFormat
-     */
-    public function nextLevel()
+    public function nextLevel(): self
     {
         if ($this->oNextLevelFormat === null) {
             $this->oNextLevelFormat = clone $this;
@@ -276,10 +271,7 @@ public function beLenient(): void
         $this->bIgnoreExceptions = true;
     }
 
-    /**
-     * @return OutputFormatter
-     */
-    public function getFormatter()
+    public function getFormatter(): OutputFormatter
     {
         if ($this->oFormatter === null) {
             $this->oFormatter = new OutputFormatter($this);