DroppedVarStats: Move InlinedAt to VarID rather than a separate map (#238936)
Fixes some false negatives with the `-dropped-variable-stats`
instrumentation which finds variables dropped from debug info.
The inlining information of a variable is part of its identity. Two
debug records with the same DILocalVariable but a different inlinedAt
must be considered different variables and their dropped status must be
computed separately.
This reuses the existing DebugVariableAggregate class to represent a
variable's identity.
Some further refactoring could be done, I only removed the now unused
parameters from the functions. This doesn't fix all false negatives, I
will put up another PR to fix the scope traversal.
Assisted-by: Claude