refactor: get hooks

[zombieJ]

抽取一个 hooks 出来，以供 Watermark 监听多子元素的场景：

<Watermark>
  <Dialog />
  <Dialog />
</Watermark>

[github-actions]

😭 Deploy PR Preview f60a3db failed. Build logs

_{🤖 By surge-preview}

[codecov]

Codecov Report

Merging #7 (68131bf) into master (1082b46) will increase coverage by 4.18%.
The diff coverage is 77.14%.

❗ Current head 68131bf differs from pull request most recent head f60a3db. Consider uploading reports for the commit f60a3db to get more accurate results

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
+ Coverage   74.19%   78.37%   +4.18%     
==========================================
  Files           2        3       +1     
  Lines          31       37       +6     
  Branches       12       13       +1     
==========================================
+ Hits           23       29       +6     
  Misses          7        7              
  Partials        1        1              

Files Changed	Coverage Δ
src/MutateObserver.tsx	76.19% <76.19%> (ø)
src/useMutateObserver.tsx	78.57% <78.57%> (ø)

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