fix: treeCheckable should support ReactNode

Author: zombieJ

src/Context.tsx

@@ -3,7 +3,7 @@ import { IconType } from 'rc-tree/lib/interface';
 import { Key, LegacyDataNode } from './interface';
 
 interface ContextProps {
-  checkable: boolean;
+  checkable: boolean | React.ReactNode;
   checkedKeys: Key[];
   halfCheckedKeys: Key[];
   treeExpandedKeys: Key[];

src/TreeSelect.tsx

@@ -191,7 +191,7 @@ const RefTreeSelect = React.forwardRef<RefSelectProps, TreeSelectProps>((props,
     onSelect,
     onDeselect,
   } = props;
-  const mergedCheckable = !!(treeCheckable || treeCheckStrictly);
+  const mergedCheckable: React.ReactNode | boolean = treeCheckable || treeCheckStrictly;
   const mergedMultiple = multiple || mergedCheckable;
   const treeConduction = treeCheckable && !treeCheckStrictly;
   const mergedLabelInValue = treeCheckStrictly || labelInValue;