slowdown in `methods(hvcat)`

[JeffBezanson]

After #41394, the call methods(hvcat, (Tuple{Int,Int},Any,Any,Any,Any,Any,Any,Int,Int)) takes over 50 seconds instead of less than 1 second. Most likely due to subtyping of lots of unions and long argument lists.

[dkarrasch]

Is this improved/resolved by #41511? Probably not.

[JeffBezanson]

I checked; unfortunately not.

[dkarrasch]

That reminds me of a massive observed slowdown when I was extending concatenation of LinearMaps toward AbstractMatrix, JuliaLinearAlgebra/LinearMaps.jl#71. Unfortunately, I forgot how it got resolved eventually, probably by pure luck, because I didn't know how to inspect the problem more thoroughly.