Merge forwardport of #11048 to 2.3-develop branch

Applied pull request patch https://github.com/magento/magento2/pull/11048.patch (created by @PieterCappelle) based on commit(s):
  1. c3ea1f5
  2. 0c0393d
  3. 6237877
  4. 202dd82

Fixed GitHub Issues in 2.3-develop branch:
  - #10417: Wysywig editor shows broken image icons (reported by @deadlyw1re)

app/code/Magento/Cms/Helper/Wysiwyg/Images.php

@@ -189,7 +189,13 @@ public function getImageHtmlDeclaration($filename, $renderAsTag = false)
                 $html = $fileUrl;
             } else {
                 $directive = $this->urlEncoder->encode($directive);
-                $html = $this->_backendData->getUrl('cms/wysiwyg/directive', ['___directive' => $directive]);
+                $html = $this->_backendData->getUrl(
+                    'cms/wysiwyg/directive',
+                    [
+                        '___directive' => $directive,
+                        '_escape_params' => false,
+                    ]
+                );
             }
         }
         return $html;

app/code/Magento/Cms/Test/Unit/Helper/Wysiwyg/ImagesTest.php

@@ -477,7 +477,7 @@ public function testGetImageHtmlDeclaration($baseUrl, $fileName, $isUsingStaticU
 
         $this->backendDataMock->expects($this->any())
             ->method('getUrl')
-            ->with('cms/wysiwyg/directive', ['___directive' => $directive])
+            ->with('cms/wysiwyg/directive', ['___directive' => $directive, '_escape_params' => false])
             ->willReturn($directive);
 
         $this->assertEquals($expectedHtml, $this->imagesHelper->getImageHtmlDeclaration($fileName));