:incomplete expression generation

[aviatesk]

# on https://github.com/JuliaLang/julia/pull/46372
julia> Base.parse_input_line("code_typed((Float64,)) do x")
:($(Expr(:error, JuliaSyntax.ParseError(JuliaSyntax.SourceFile("code_typed((Float64,)) do x", "none", [1, 28]), JuliaSyntax.Diagnostic[JuliaSyntax.Diagnostic(28, 27, :error, "premature end of input"), JuliaSyntax.Diagnostic(28, 27, :error, "Expected `end`")]))))

# on master
julia> Base.parse_input_line("code_typed((Float64,)) do x")
:($(Expr(:incomplete, "incomplete: premature end of input")))

This difference disallows REPL to accept multi-line inputs on JuliaLang/julia#46372, e.g.

julia> code_typed((Float64,)) do x<<<RET>>>
ERROR: ParseError:
Error: premature end of input
@ REPL[16]:2:1
code_typed((Float64,)) do x
Error: Expected `end`
@ REPL[16]:2:1
code_typed((Float64,)) do x

[pfitzseb]

Dup of #42.