show current-world number of methods for display(::Function)

[stevengj]

Functions are displayed in the REPL as foo (generic function with N methods). Before this PR, N was the number of methods ever defined, even methods that have been overwritten. After this PR, N is the number in the current world, matching the number displayed by methods(foo).

Before this PR:

julia> f(x) = 3
f (generic function with 1 method)

julia> f(x) = 4
WARNING: Method definition f(Any) in module Main at REPL[1]:1 overwritten at REPL[2]:1.
f (generic function with 2 methods)

After this PR:

julia> f(x) = 3
f (generic function with 1 method)

julia> f(x) = 4
WARNING: Method definition f(Any) in module Main at REPL[1]:1 overwritten at REPL[2]:1.
f (generic function with 1 method)

(Note that #19888 eliminates the warning.)

[JeffBezanson]

(fixes #19781)