julia

ca7b9c37 - Make concatenation of SubString{AnnotatedString} preserve annotations (#51806)

Make concatenation of SubString{AnnotatedString} preserve annotations (#51806) `SubStrings` have been overlooked, and thanks to a few compiler quirks (relating to inlining and effect analysis), adding support for them is unfortunately a little more complicated than adding a `|| s isa SubString{<:AnnotatedString}` clause thanks to the new generated runtime-checks. To maintain the zero-overhead non-annotated code path, we need to implement a separate function `_isannotated`, which we also make use of to simplify the current join method.