* fix(components): [el-form] validation with callbacks throws
- Fix Form component's validation with callbacks still throws error
- Fix FormItem component's validation with callbacks still throws error
- Update test cases to make sure this functionality's integrity
* Fix linter
* fix(components): [el-form] Form not emitting validation result
- Refactor validate code to allow it to yield promise value
- Update tests accordingly
* fix: refactor
Co-authored-by: 三咲智子 <sxzz@sxzz.moe>