feat(comp: space): replace gap prop with size

[liuzaijiang]

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• The commit message follows our guidelines
• Tests for the changes have been added/updated or not needed
• Docs and demo have been added/updated or not needed

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What kind of change does this PR introduce?

• Bugfix
• Feature
• Component style update
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Application (the showcase website) / infrastructure changes
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更新back-top less变量

[idux-bot]

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[danranVm]

这是一个破坏性变更，需要在 commit 的 breaking changes 里声明一下

[codecov]

Codecov Report

Merging #670 (1479892) into main (84116bd) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #670      +/-   ##
==========================================
+ Coverage   83.92%   83.95%   +0.03%     
==========================================
  Files         396      396              
  Lines        9909     9918       +9     
  Branches     2278     2281       +3     
==========================================
+ Hits         8316     8327      +11     
+ Misses       1593     1591       -2     

Impacted Files	Coverage Δ
packages/components/space/index.ts	100.00% <ø> (ø)
packages/components/space/src/types.ts	100.00% <ø> (ø)
packages/components/config/src/defaultConfig.ts	100.00% <100.00%> (ø)
packages/components/space/src/Space.tsx	94.91% <100.00%> (+0.17%)	⬆️
packages/components/utils/src/useFormElement.ts	95.65% <0.00%> (ø)
packages/components/modal/src/ModalWrapper.tsx	74.01% <0.00%> (+0.20%)	⬆️
packages/cdk/a11y/src/inputModalityDetector.ts	84.00% <0.00%> (+6.72%)	⬆️

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[danranVm]

LGTM