feat: bigint for the DefinePlugin plugin

[alexander-akait]

What kind of change does this PR introduce?

features (bigint can be regarded as a fix):

• support BigInt for DefinePlugin
• improve typeof for null
• improve null comparison

Also we already fix undefined and array behavior for webpack@5, so after merge we can close #10425

What needs to be documented once your changes are merged?

Nothing

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[webpack-bot]

@evilebottnawi Thanks for your update.

I labeled the Pull Request so reviewers will review it again.

@sokra Please review the new changes.

[webpack-bot]

Thank you for your pull request! The most important CI builds succeeded, we’ll review the pull request soon.

[webpack-bot]

The minimum test ratio has been reached. Thanks!

[alexander-akait]

Done

[alexander-akait]

/cc @sokra conflicts fixed, will be great to merge it so that I can continue to improve and avoid conflicts

[sokra]

Thanks