Implement readonly for `TextFieldSimpleComponent`

docs/release-notes-player.txt

 Player
 ======
 1.20.0
+- Implement readonly fot text fields of cloze elements
 - Fix height of elements with dynamic positioning and fixed size
 - Fix dimensions of image elements with dynamic positioning and fixed size
 - Fix display of fixed size dynamic elements on iPad

projects/common/ui-elements/textfield-simple/text-field-simple.component.ts

@@ -15,6 +15,7 @@ import { TextFieldSimpleElement } from './text-field-simple-element';
            [style.font-weight]="elementModel.fontProps.bold ? 'bold' : ''"
            [style.font-style]="elementModel.fontProps.italic ? 'italic' : ''"
            [style.text-decoration]="elementModel.fontProps.underline ? 'underline' : ''"
+           [readonly]="elementModel.readOnly"
            [formControl]="elementFormControl"
            value="{{elementModel.value}}">
   `,