fix(FormItem): model should update before event call

[xachary]

General

根据 #3570 排查得知，FormItem 内部是先触发表单组件的 event，后更新 model，导致 getFormValues 及其依赖了它的例如 reload 方法没有获得最新的 model 值。现调整为优先更新 model。

• Pull request template structure not broken

Type

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

ℹ️ Check all checkboxes - this will indicate that you have done everything in accordance with the rules in CONTRIBUTING.

• My code follows the style guidelines of this project
• Is the code format correct
• Is the git submission information standard?
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[wangjue666]

@xachary bug修复等紧急问题要合并PR, 可以艾特下我跟 @likui628

[xachary]

@xachary bug修复等紧急问题要合并PR, 可以艾特下我跟 @likui628

好的~