[lldb][DataFormatter] Surface CalculateNumChildren errors in std::vector summary (#135944)

When the data-formatters happen to break (e.g., due to layout changes in
libc++), there's no clear indicator of them failing from a user's
perspective. E.g., for `std::vector`s we would just show:
```
(std::vector<int>) v = size=0 {}
```
which is highly misleading, especially if `v.size()` returns a non-zero
size.

This patch surfaces the various errors that could occur when calculating
the number of children of a vector.

rdar://146964266

0 files changed, 0 insertions, 0 deletions