Synthetic providers for collection types use a child name format of
"[N]".
This `ValueObjectSynthetic` to automatically convert child names in this
convention to the index embedded in the subscript string. With this
change, synthetic formatters for collections will only need to implement
`GetIndexOfChildWithName` or `get_child_index` for non-indexed
collection children. Some examples of non-indexed children are
`$$dereference$$` support, or "hidden" children.
The automatic conversion applies to N values that are less than the
number of children reported by the synthetic provider.
Vector registers have synthetic values for display purposes. This causes
SBValue::GetExpressionPath to dispatch
to ValueObjectSynthetic instead of ValueObjectRegister, producing
incorrect results.
Fixes#147144
