fixup! Revert "Highlight julia-repl code in Markdown specially (#54423)"

Author: KristofferC

stdlib/Markdown/src/Common/block.jl

@@ -39,7 +39,7 @@ end
 # Headers
 # –––––––
 
-mutable struct Header{level}
+mutable struct Header{level} <: MarkdownElement
     text
 end
 

stdlib/Markdown/src/Common/inline.jl

@@ -4,7 +4,7 @@
 # Emphasis
 # ––––––––
 
-mutable struct Italic
+mutable struct Italic <: MarkdownElement
     text
 end
 
@@ -20,7 +20,7 @@ function underscore_italic(stream::IO, md::MD)
     return result === nothing ? nothing : Italic(parseinline(result, md))
 end
 
-mutable struct Bold
+mutable struct Bold <: MarkdownElement
     text
 end
 
@@ -66,7 +66,7 @@ end
 # Images & Links
 # ––––––––––––––
 
-mutable struct Image
+mutable struct Image <: MarkdownElement
     url::String
     alt::String
 end
@@ -85,7 +85,7 @@ function image(stream::IO, md::MD)
     end
 end
 
-mutable struct Link
+mutable struct Link <: MarkdownElement
     text
     url::String
 end
@@ -156,7 +156,7 @@ end
 # Punctuation
 # –––––––––––
 
-mutable struct LineBreak end
+mutable struct LineBreak <: MarkdownElement end
 
 @trigger '\\' ->
 function linebreak(stream::IO, md::MD)