Libdl: Store path contents as `Tuple` instead of `Vector` (#57734)
This makes `LazyLibraryPath` eligible for const-prop, which is important
so that we can inline/infer `string(::LazyLibraryPath)` at compile-time
if the argument is a (global) `const`.
Otherwise, this code is not infer-able without something like
TypedCallable to make the interface requirements explicit.