refactor(v2): replace few Lodash methods with native counterparts

[Simek]

Motivation

This is a reworked version of #2520 PR, same motivation like in previous PRs.

This is the initial step in getting rid of main lodash package in favour of single method ones in core v2 Docusaurus package. In this PR _.assign, _.compact, _.flatten and _.isArray methods has been replaced with their native counterparts.

After applying those changes only has, isPlainObject and isString lodash packages are needed in the core.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Same test results before and after code refactor.

Related PRs

• refactor(v2): use single method package instead of whole Lodash package in blog plugin #2460
• chore(v2): use single method Lodash packages in docs plugin #2519
• chore(v2): replace few Lodash methods with native counterparts #2520

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