Support convert(LineNumberNode, ::LineInfoNode) (#50676)

xref timholy/CodeTracking.jl#113. It
looks like that method might not even be important anymore for
CodeTracking and the Revise stack, but because we have lots of packages
that dive into internals, having this seems to make sense.

base/expr.jl

@@ -33,6 +33,9 @@ macro gensym(names...)
     return blk
 end
 
+## line numbers ##
+convert(::Type{LineNumberNode}, lin::Core.LineInfoNode) = LineNumberNode(Int(lin.line), lin.file)
+
 ## expressions ##
 
 isexpr(@nospecialize(ex), head::Symbol) = isa(ex, Expr) && ex.head === head

test/core.jl

@@ -8044,3 +8044,7 @@ end
 # `SimpleVector`-operations should be concrete-eval eligible
 @test Core.Compiler.is_foldable(Base.infer_effects(length, (Core.SimpleVector,)))
 @test Core.Compiler.is_foldable(Base.infer_effects(getindex, (Core.SimpleVector,Int)))
+
+let lin = Core.LineInfoNode(Base, first(methods(convert)), :foo, Int32(5), Int32(0))
+    @test convert(LineNumberNode, lin) == LineNumberNode(5, :foo)
+end