Implement dsize function for `fstring_table_type`

The fstring table size used to be reported as part of the VM
size, but since it was refactored to be lock-less it was no
longer reported.

Since it's now wrapped by a `T_DATA`, we can implement its
`dsize` function and get a valuable insight into the size
of the table.

```
{"address":"0x100ebff18", "type":"DATA", "shape_id":0, "slot_size":80,
"struct":"VM/fstring_table", "memsize":131176, ...
```

0 files changed, 0 insertions, 0 deletions