Make :([x; y, z]) parseable

[pablosanjose]

To make DSLs one needs to use a syntax that is parseable, so that macros can ingest it
I'm trying to make a @mymacro distinguish between @mymacro((x; kw1=1, kw2=2) -> ...) and @mymacro([x; kw1=1, kw2=2] -> ...). I can make it work with @mymacro([x, y; kw1=1, kw2=2] -> ...) but not with a single positional argument.

The reason is that :([x; y, z]) is not parseable, but :([x, y; z, w]) and even:([x,; y, z]) are

julia> :([x; y, z])
ERROR: ParseError:
# Error @ REPL[1]:1:8
:([x; y, z])
#      ╙ ── unexpected comma in array expression
Stacktrace:
 [1] top-level scope
   @ none:1

julia> :([x,; y, z])
:([$(Expr(:parameters, :y, :z)), x])

After confirming on slack that this change would not be breaking, I'd like to propose to make :([x; y, z]) parseable