compiler: add '$' to names in expression export data

compiler: add '$' to names in expression export data

    For inlined function bodies we're going to need to refer to variables,
    so change the existing export data to add a '$' to names that look
    like identifiers: true, false, nil, convert.

    While we're here drop an unnecessary space character after operators.

    Reviewed-on: https://go-review.googlesource.com/c/150067

From-SVN: r266529