Add test for nested template types

[hallfox]

It seems that generating a type with a member function that uses a reference to a typedef of a templated type causes autocxx to interpret the class with the typedef member as a namespace.

The extern "C++" generated the following from the submitted test case:

unsafe extern "C++" {
    #[cxx_name = "B"]
    type B = super::B;

    #[namespace = "B"]
    #[cxx_name = "F"]
    type B_F;
}

Which I believe is what causes the downstream issue that gets reported in the test failure:

cargo:warning=/tmp/.tmpTCdyDa/target/cxx/gen0.cxx:120:11: error: 'namespace B { }' redeclared as different kind of entity
cargo:warning=  120 | namespace B {
cargo:warning=      |           ^
cargo:warning=In file included from /tmp/.tmpTCdyDa/target/cxx/gen0.cxx:1:
cargo:warning=/tmp/.tmpTCdyDa/input.h:5:7: note: previous declaration 'class B'
cargo:warning=    5 | class B {
cargo:warning=      |       ^

I tried poking around RsCodeGenerator::generate_cxxbridge_type, which is where I think the actual generation of the buggy #[namespace = "B"] is coming from, but I don't really understand enough about how the namespace is being parsed to suggest a fix.

Maybe this is a known issue? There's some comments scattered around the source that seem to imply that some tricks are being done to handle nested types.

May be related to #1350

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