insorted behaves differently than in

[LilithHafner]

julia> insorted(-2, [1,2,3], by=abs)
true

julia> in(-2, [1,2,3])
false

insorted is documented to return true iff x is == to an element of the collection. It actually returns true if x is neither less than nor greater than an element of the collection. We could

1. add an == check that fixes this bug with a runtime penalty
2. document the current behavior as expected

[LilithHafner]

Duplicate of #44102