Document webpack change: add __webpack_module__ and __webpack_module_id__ to the api

[webpack-bot]

A pull request by @sokra was merged and maintainers requested a documentation change.

See pull request: webpack/webpack#15282

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What kind of change does this PR introduce?
feature

Did you add tests for your changes?
yes

Does this PR introduce a breaking change?
no

What needs to be documented once your changes are merged?

• __webpack_module__ equals to module but is always available (module is not available in strict ESM)
• __webpack_module__.id equals to module.id but is always available (module is not available in strict ESM)

[snitin315]

I will add it.

[sokra]

Update: It was changed from __webpack_module_id__ to __webpack_module__.id