picker的modalTitle属性应当与dialog的title属性类似，支持配置schema

#### 是否关联于某个问题吗：
picker组件的modalTitle属性只支持字符串，无法实现增加副标题的需求
#### 预期的解决方案：
仿照dialog组件的title属性

Start by locating the picker component's modalTitle handling and the dialog component's title schema support. Compare how each title is configured, then add equivalent schema support for picker so a subtitle can be configured. Confirm that existing string titles continue to work and that the requested subtitle configuration is accepted.

Written by the indexing model from the issue text.