[Fix]: remove switch component hasEmpty logic

[nonzzz]

Checklist

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• [x] Fix linting errors
• [x] Tests have been added / updated (or snapshots)

Change information

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• Remove hasEmpty logic, because user specify a custom value. it will cause the internal logic confusion.
• Remove useless computed logic.
• Change manual control data flow logic. In past, we will auto set internal value by watchEffect,But it unreasonable, So change it, Now the internal logic will be:

 watchEffect(() => {
      if (props.value) {
        setCurrentValue(props.value)
      }
 })

• Change internal value variable name from value => currentValue.

[codecov[bot]]

Codecov Report

Merging #218 (afd4cd9) into master (67246f7) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #218   +/-   ##
=======================================
  Coverage   96.61%   96.61%           
=======================================
  Files         184      184           
  Lines        2068     2068           
  Branches      358      357    -1     
=======================================
  Hits         1998     1998           
  Misses         70       70           

Impacted Files	Coverage Δ
packages/vue/src/switch/index.ts	100.00% <ø> (ø)
packages/vue/src/switch/switch.tsx	100.00% <100.00%> (ø)

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