refactor(Textarea): rename private property (#5504)

Author: ArgoZhang

src/BootstrapBlazor/Components/Textarea/Textarea.razor

@@ -8,4 +8,4 @@
 }
 <textarea @attributes="AdditionalAttributes" placeholder="@PlaceHolder" id="@Id" class="@ClassName" disabled="@Disabled"
           @bind-value="CurrentValueAsString" @bind-value:event="@EventString" @onblur="@OnBlur"
-          data-bb-shift-enter="@_shiftEnterString" data-bb-scroll="@AutoScrollString" @ref="FocusElement"></textarea>
+          data-bb-shift-enter="@ShiftEnterString" data-bb-scroll="@AutoScrollString" @ref="FocusElement"></textarea>

src/BootstrapBlazor/Components/Textarea/Textarea.razor.cs

@@ -45,7 +45,7 @@ public partial class Textarea
     /// </summary>
     private string? AutoScrollString => IsAutoScroll ? "auto" : null;
 
-    private string? _shiftEnterString => UseShiftEnter ? "true" : null;
+    private string? ShiftEnterString => UseShiftEnter ? "true" : null;
 
     /// <summary>
     /// <inheritdoc/>