Dynamic Matrix - Add a note that the allowRowsDragAndDrop option is available only when columnLayout is horizontal

[JaneSjs]

User Issue: T15091 - Dynamic Matrix: Dynamic Matrix allow Drag and Drop in Vertical Layout
https://surveyjs.answerdesk.io/internal/ticket/details/T15091

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survey-library/src/question_matrixdynamic.ts

Line 268 in 8c9a0c0

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The row reordering option is available when a Dynamic Matrix appears in a default horizontal column layout (columnLayout = 'horizontal'). Here is a code snippet from our source code: allowRowsDragAndDrop. However, the doc description doesn't mention this specific.