Add methods min, max, minmax taking only single Dates.AbstractTime (#32525)

Methods `min`, `max` and `minmax` should also be able to take just one
`Dates.AbtractTime` argument. See discussion:
https://discourse.julialang.org/t/max-and-min-of-single-dates/26074

Author: pfarndt

stdlib/Dates/src/types.jl

@@ -403,6 +403,9 @@ function ==(a::Time, b::Time)
         microsecond(a) == microsecond(b) && nanosecond(a) == nanosecond(b)
 end
 (==)(x::TimeType, y::TimeType) = (===)(promote(x, y)...)
+Base.min(x::AbstractTime) = x
+Base.max(x::AbstractTime) = x
+Base.minmax(x::AbstractTime) = (x, x)
 Base.hash(x::Time, h::UInt) =
     hash(hour(x), hash(minute(x), hash(second(x),
         hash(millisecond(x), hash(microsecond(x), hash(nanosecond(x), h))))))

stdlib/Dates/test/types.jl

@@ -228,6 +228,23 @@ end
     @test Dates.Date(Dates.DateTime(Dates.Date(2012, 7, 1))) == Dates.Date(2012, 7, 1)
 end
 
+@testset "min and max" begin
+    for (a, b) in [(Dates.Date(2000), Dates.Date(2001)),
+                    (Dates.Time(10), Dates.Time(11)),
+                    (Dates.DateTime(3000), Dates.DateTime(3001)),
+                    (Dates.Week(42), Dates.Week(1972))]
+        @test min(a, b) == a
+        @test min(b, a) == a
+        @test min(a) == a
+        @test max(a, b) == b
+        @test max(b, a) == b
+        @test max(b) == b
+        @test minmax(a, b) == (a, b)
+        @test minmax(b, a) == (a, b)
+        @test minmax(a) == (a, a)
+    end
+end
+
 @testset "issue #31524" begin
     dt1 = Libc.strptime("%Y-%M-%dT%H:%M:%SZ", "2018-11-16T10:26:14Z")
     dt2 = Base.Libc.TmStruct(14, 30, 5, 10, 1, 99, 3, 40, 0)