[tune] Fix hyperopt points to evaluate for nested lists

[krfricke]

Why are these changes needed?

Internal hyperopt parameter names are flattened for lists (e.g. nested/0, nested/1). However, when supplying points_to_evaluate, we have to flatten those names as well, as they otherwise cannot be mapped to the internal names.

Related issue number

Closes #14470

Checks

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• Testing Strategy
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