doc(TableSearch): update search documentation (#4840)

* doc: update search document

* refactor: 重构 SelectedRow

Author: ArgoZhang

src/BootstrapBlazor.Shared/Components/Samples/Table/TablesSearch.razor.cs

@@ -148,8 +148,7 @@ private Task<QueryData<Foo>> OnQueryAsync(QueryPageOptions options)
     {
         // 使用内置扩展方法 ToFilter 获得过滤条件
         // 目前 ToFilterFunc 无法解决大小写敏感问题
-        // var items = Items.Where(options.ToFilterFunc<Foo>());
-        IEnumerable<Foo> items = Items;
+        var items = Items.Where(options.ToFilterFunc<Foo>());
         if (!string.IsNullOrEmpty(options.SearchText))
         {
             // 使用 Linq 处理

src/BootstrapBlazor/Components/SelectGeneric/SelectGeneric.razor

@@ -22,7 +22,7 @@
             }
             else
             {
-                <input type="text" id="@InputId" disabled="@Disabled" placeholder="@PlaceHolder" class="@InputClassString" value="@SelectedRow?.Text" @onchange="OnChange" readonly="@ReadonlyString" />
+                <input type="text" id="@InputId" disabled="@Disabled" placeholder="@PlaceHolder" class="@InputClassString" value="@SelectedRow.Text" @onchange="OnChange" readonly="@ReadonlyString" />
             }
             <span class="@AppendClassString"><i class="@DropdownIcon"></i></span>
         </div>

src/BootstrapBlazor/Components/SelectGeneric/SelectGeneric.razor.cs

@@ -277,7 +277,7 @@ private List<SelectedItem<TValue>> Rows
         }
     }
 
-    private SelectedItem<TValue>? SelectedRow
+    private SelectedItem<TValue> SelectedRow
     {
         get
         {
@@ -286,7 +286,7 @@ private SelectedItem<TValue>? SelectedRow
         }
     }
 
-    private SelectedItem<TValue>? GetSelectedRow()
+    private SelectedItem<TValue> GetSelectedRow()
     {
         var item = Rows.Find(i => Equals(i.Value, Value))
             ?? Rows.Find(i => i.Active)