fix(nodemaintemplate): resolve async chunk path platform agnostic

[kwonoj]

What kind of change does this PR introduce?

closes #8032.

For async-node target, it creates template to resolve path to chunk bundles via string concat, ends up creating slash-mixed paths on windows platform, fail to some tools like vs code resolves correct sources. This PR updates template to use path.resolve instead to have platform agnostic path resolving behavior. getAssetPath still generates using fixed separator in slashes, but let it just correctly resovled via path.resolve directly instead of trying to make changes to those logics.

Did you add tests for your changes?

• manually verified behavior, bit unsure where would be best to add test cases for this.

Does this PR introduce a breaking change?

No.

What needs to be documented once your changes are merged?

[jsf-clabot]

All committers have signed the CLA.

[webpack-bot]

For maintainers only:

• This need to be documented (issue in webpack/webpack.js.org will be filed when merged)

[webpack-bot]

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

[sokra]

Thanks