Set the visitInnerUses flag. This is only a quick, partial fix.
InteriorUseWalker does not generate complete liveness for two reasons
1. pointer escapes. The client must always check for escapes before assuming
complete liveness.
2. dead end blocks. Until we have complete OSSA lifetimes, the algorithm for
handling nested borrows is incorrect. The visitInnerUses flag works around this
problem, but it isn't well tested and I'm not sure it's properly records escapes yet.
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