Document webpack change: add alias to false (ignore) and alias to array

[webpack-bot]

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

See pull request: webpack/webpack#9380

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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?
resolve.alias now supports:

• false: to ignore a module (replaced with empty module)
• array of strings: to offer multiple alternatives with are tried. Makes most sense when different subpaths.

[sokra]

done