refactor: drop lodash for lib/hexo/index.js

[SukkaW]

What does it do?

This PR is part of #3753

This PR only replace cloneDeep and debounce with native while lodash itself retains exposed to global.

How to test

git clone -b drop-lodash-for-index https://github.com/sukkaw/hexo.git
cd hexo
npm install
npm test

Screenshots

The performance is more or less the same after this PR.

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[coveralls]

Coverage increased (+0.01%) to 97.158% when pulling 9576f42 on SukkaW:drop-lodash-for-index into 1b69a53 on hexojs:master.

[curbengh]

Tested Object.assign on default_config.js.

[curbengh]

Please verify the benchmark (rebase first) before merging.

[SukkaW]

@curbengh Last time I check, the benchmark seems no difference. I will trigger a rebuild to see if there is any regression.

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Benchmark result:

Node.js 8

	Process Time	Memory
Current Master Branch	30.6s	671MB
This PR	31.4s	678MB

Node.js 10

	Process Time	Memory
Current Master Branch	25.1s	628MB
This PR	26.8s	629MB

Node.js 12

	Process Time	Memory
Current Master Branch	25.1s	707MB
This PR	26.8s	801MB

Node.js 13

	Process Time	Memory
Current Master Branch	25.2s	805MB
This PR	25.6s	770MB

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I think it is ok to merge. There is no significant performance impact.