Document the kind of indices returned by `findmin`/`findmax`/`argmin`/`argmax` (#46705)
This is the sentence used for `find*` functions, introduced by #25577.
Also change "the domain of `f`" to "`domain`" as the domain of `f` can
be a superset of the passed `domain`.
(Spotted at https://github.com/JuliaData/DataFrames.jl/issues/3139.)
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Co-authored-by: Jameson Nash <vtjnash@gmail.com>
Co-authored-by: Lilith Orion Hafner <lilithhafner@gmail.com>