Add missing type parameter to TakeWhile (#42958)

Without this `TakeWhile` has `eltype` of `Any`

(cherry picked from commit ab0c6dd)

Author: pepijndevos

base/iterators.jl

@@ -779,7 +779,7 @@ end
 
 IteratorSize(::Type{<:TakeWhile}) = SizeUnknown()
 eltype(::Type{TakeWhile{I,P}} where P) where {I} = eltype(I)
-IteratorEltype(::Type{TakeWhile{I}} where P) where {I} = IteratorEltype(I)
+IteratorEltype(::Type{TakeWhile{I, P}} where P) where {I} = IteratorEltype(I)
 
 
 # dropwhile

test/iterators.jl

@@ -201,6 +201,7 @@ end
     @test collect(takewhile(_->true,5:10)) == 5:10
     @test collect(takewhile(isodd,[1,1,2,3])) == [1,1]
     @test collect(takewhile(<(2), takewhile(<(3), [1,1,2,3]))) == [1,1]
+    @test Base.IteratorEltype(typeof(takewhile(<(4),Iterators.map(identity, 1:10)))) isa Base.EltypeUnknown
 end
 
 # dropwhile
@@ -213,6 +214,7 @@ end
     @test isempty(dropwhile(_->true, 1:3))
     @test collect(dropwhile(isodd,[1,1,2,3])) == [2,3]
     @test collect(dropwhile(iseven,dropwhile(isodd,[1,1,2,3]))) == [3]
+    @test Base.IteratorEltype(typeof(dropwhile(<(4),Iterators.map(identity, 1:10)))) isa Base.EltypeUnknown
 end
 
 # cycle