Dependencies: Set prefer-dedupe true in npm configuration

[sirreal]

This change was applied in Gutenberg:

WordPress/gutenberg#61630

Quoting that PR:

The npm dedupe command searches
and attempts to simplify the overall structure of the local package
tree to allow dependent packages to be shared more effectively. As
detailed in #61532, reducing the amount of dependency duplication is
beneficial for a few reasons:

• Fewer packages overall.
• Faster installation.
• Less size to transfer and store on disk.
• Usually bundle size is reduced (although this depends on which
  versions of packages are used).

However, unless the command is run regularly, the project's dependency
tree easily falls out of order.

See https://docs.npmjs.com/cli/v10/commands/npm-dedupe

Trac ticket: https://core.trac.wordpress.org/ticket/62190

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Props jonsurrell, desrosj.

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[sirreal]

I've created another PR that performs npm dedupe: #7538

[desrosj]

Let's merge this change into #7538. I think it's fine to handle in the same commit!

[sirreal]

Sounds good, now that #7526 has landed there shouldn't be any conflicts 👍

[sirreal]

Superseded by #7538.