feat(signature): support tips slot

Author: chouchouji

packages/vant/src/signature/README.md

@@ -99,6 +99,12 @@ Use `background-color` prop to set the color of the background.
 | submit | Emitted when clicking the confirm button | _data: { image: string; canvas: HTMLCanvasElement }_ |
 | clear | Emitted when clicking the cancel button | - |
 
+### Slots
+
+| Name | Description | SlotProps |
+| ---- | ----------- | --------- |
+| tips | Custom tips | -         |
+
 ### Methods
 
 Use [ref](https://vuejs.org/guide/essentials/template-refs.html) to get Signature instance and call instance methods.

packages/vant/src/signature/README.zh-CN.md

@@ -99,6 +99,12 @@ export default {
 | submit | 点击确定按钮时触发 | _data: { image: string; canvas: HTMLCanvasElement }_ |
 | clear | 点击取消按钮时触发 | - |
 
+### Slots
+
+| 名称 | 说明           | 参数 |
+| ---- | -------------- | ---- |
+| tips | 自定义提示文案 | -    |
+
 ### 方法
 
 通过 ref 可以获取到 Signature 实例并调用实例方法，详见[组件实例方法](#/zh-CN/advanced-usage#zu-jian-shi-li-fang-fa)。

packages/vant/src/signature/Signature.tsx

@@ -53,7 +53,7 @@ export default defineComponent({
 
   emits: ['submit', 'clear', 'start', 'end', 'signing'],
 
-  setup(props, { emit }) {
+  setup(props, { emit, slots }) {
     const canvasRef = ref<HTMLCanvasElement>();
     const wrapRef = ref<HTMLElement>();
     const ctx = computed(() => {
@@ -195,6 +195,8 @@ export default defineComponent({
               onTouchmove={touchMove}
               onTouchend={touchEnd}
             />
+          ) : slots.tips ? (
+            slots.tips()
           ) : (
             <p>{props.tips}</p>
           )}