[CXX Interoperability] Stop re-importing FuncDecl when FuncDecl is imported before parent record (#59607)
We saw a test case failing when 2 records contain the same operator. This occurs because when the first operator is called, we import the record associated with that operator but we also import the _function_ for the 2nd record. So if we have 2 records `Foo` and `Bar` and both implement `operator-`, after calling `Foo`'s `operator-` we would have imported
1. `Foo`
2. `Foo.operator-`
3. `Bar.operator-`
Then when we call `Bar.operator-` we try importing `Bar` record & then import the operator again. So that ends up with
1. `Foo`
2. `Foo.operator-`
3. `Bar.operator-`
4. `Bar`
5. `Bar.operator-`
which causes there to be 2 imports of the same operator (`FuncDecl`)
This patch checks to see if the `FuncDecl` was previously imported and returns early if it has been
Thanks @egorzhdan and @zoecarver for helping me debug this one :p