Introduce an option to disable inplace editing for form string elements

[JaneSjs]

• T21012 - Remove editing from body title and description and keep it in side panel (property grid)
  https://surveyjs.answerdesk.io/internal/ticket/details/T21012
• T21022 - Rich Text Support in Creator
  https://surveyjs.answerdesk.io/internal/ticket/details/T21022
• T15725 - How to disabled design surface's description?
  https://surveyjs.answerdesk.io/internal/ticket/details/T15725

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Since custom editors do not appear in inplace editing, if we enable Rich Text Formatting, the following appears when users try to edit the text on a design surface:

Consider introducing an option to disable inplace editing to prevent users from manually updating a plain RTF text.