[C++20] [Modules] Handle modules visible relationship properly

Close https://github.com/llvm/llvm-project/issues/62589.

Previously, for global module fragments, we will justify if it is
visible by the visibility of their top level parents. But this is an
overkill, it is problematic if we have a deduction guide in the global
module fragments. See the attached test for example. In this example, we
will mark the global module fragments as visible, but our old strategy
will miss the case surprisingly due to we will only search for the top
level modules.

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