11623: fix: Add type variable table to InferenceTableSnapshot r=flodiebold a=tysg
Fixes#11601.
I observed that removing the `rollback` line in 6fc3d3aa4c fixes the issue.
Looking at the stacktrace, I believe not restoring `type_variable_table` causes `type_variable_table` and `var_unification_table` to go out of sync, then when `hir_ty::infer::unify::InferenceTable::new_var` tries to extend `type_variable_table` to be the same length as `var_unification_table`, problems will arise.
However, I cannot pinpoint exactly how or where the vector capacity overflow happens, so my understanding might not be correct after all.
Co-authored-by: Tianyi Song <42670338+tysg@users.noreply.github.com>
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