fix(element): correct typing of method map()

[RomkeVdMeulen]

The elementFinder and index arguments of the mapping function passed to ElementArrayFinder.map() will never be undefined.

Fixes #4548

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[RomkeVdMeulen]

I signed it!

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[JacobPatenaude-AI]

I'm not sure if this PR is still active, but should each also have its typings changed?