Ignore ANSI colour codes in printing Diagonal, etc (#47430)

(cherry picked from commit 9f572b6)

Author: mcabbott

base/arrayshow.jl

@@ -40,7 +40,7 @@ centered cdot, used in printing of structural zeros of structured matrices.
 Accept keyword args `c` for alternate single character marker.
 """
 function replace_with_centered_mark(s::AbstractString;c::AbstractChar = '⋅')
-    N = length(s)
+    N = textwidth(ANSIIterator(s))
     return join(setindex!([" " for i=1:N],string(c),ceil(Int,N/2)))
 end
 

test/show.jl

@@ -2368,3 +2368,7 @@ Base.show(io::IO, ces::⛵) = Base.print(io, '⛵')
 @test Base.alignment(stdout, ⛵()) == (0, 2)
 @test Base.alignment(IOContext(IOBuffer(), :color=>true), ColoredLetter()) == (0, 1)
 @test Base.alignment(IOContext(IOBuffer(), :color=>false), ColoredLetter()) == (0, 1)
+
+# spacing around dots in Diagonal, etc:
+redminusthree = sprint((io, x) -> printstyled(io, x, color=:red), "-3", context=stdout)
+@test Base.replace_with_centered_mark(redminusthree) == Base.replace_with_centered_mark("-3")