NA dimensions for complex and tuple types

[SteveBronder]

Describe the bug

When calling $draws() on a fit object whose model has complex or tuple types in it I receive warning messages about NA's being made for the variable sizes.

To Reproduce

I made the stan program below to test this

parameters {
  real real_p;
  vector[2] vector_p;
  matrix[2, 2] matrix_p;
  array[2] matrix[2, 2] array_matrix_p;
  corr_matrix[2] corr_p;
  complex complex_p;
  complex_matrix[2, 2] complex_matrix_p;
  complex_vector[4] complex_vector_p;
  tuple(real, vector[3], array[2] matrix[2, 2], complex) tuple_int_vector_arraymatrix_complex_p;
  array[2] tuple(real, tuple(vector[2], array[2] tuple(real, complex, matrix[2, 2]))) arraytuple_big_p;
}

You can get the error with the following

# I put this in the tests/testthat/resources/stan folder
mod_params <- testing_model("parameter_types")
fit <- mod_params$pathfinder(data=data_list, seed=1234, refresh = 0)
foo = fit$draws(format = "df")
# Warning messages:
# 1: In variable_dims(metadata$variables) : NAs introduced by coercion
# 2: In variable_dims(metadata$variables) : NAs introduced by coercion
# 3: In variable_dims(metadata$variables) : NAs introduced by coercion
# 4: In variable_dims(metadata$variables) : NAs introduced by coercion
# 5: In variable_dims(metadata$variables) : NAs introduced by coercion
meta = fit$metadata()
meta$stan_variable_sizes
## Output
$lp_approx__
[1] 1

$lp__
[1] 1

$real_p
[1] 1

$vector_p
[1] 2

$matrix_p
[1] 2 2

$array_matrix_p
[1] 2 2 2

$corr_p
[1] 2 2

$complex_p
[1] NA

$complex_matrix_p
[1]  2  2 NA

$complex_vector_p
[1]  4 NA

$`tuple_int_vector_arraymatrix_complex_p:1`
[1] 1

$`tuple_int_vector_arraymatrix_complex_p:2`
[1] 3

$`tuple_int_vector_arraymatrix_complex_p:3`
[1] 2 2 2

$`tuple_int_vector_arraymatrix_complex_p:4`
[1] NA

$arraytuple_big_p
[1] NA NA  2  2

Expected behavior

Tuples and complex types would have the correct size

Operating system
Linux redhat

CmdStanR version number
master 28329d7

Additional context
I found this while working on the functions for adding pathfinder types