[BUG] emitted initialisation of base class in member initialiser list of derived copy constructor does not compile #402

Describe the bug
If, within a class hierarchy, a derived type has an operator=: (out this, that), then the lowered cpp1 code will attempt to initialise the base class using that.Base as if Base were a member.

To Reproduce
Steps to reproduce the behavior:

1. Sample code - distilled down to minimal essentials please
   The following cpp2 code:

Base : type = {
    operator=: (out this, that) = {}
}

Derived : type = {
    this: Base = ();
    operator=: (out this, that) = {}
}

will produce the following function definition for the copy constructor of Derived in cpp1:

    Derived::Derived(Derived const& that)
                                   : Base{ that.Base }
    {}

This will not compile.
2. Command lines including which C++ compiler you are using
cppfront is compiled with gcc12 and executed using

cppfront -p my_file.cpp2 -o stdout

The emitted cpp1 is also being compiled with gcc12.

3. Expected result - what you expected to happen
   I would expect the copy constructor to be emitted as

    Derived::Derived(Derived const& that)
                                   : Base{ that }
    {}

and that the emitted code would compile

4. Actual result/error5.
   The emitted code refers to the base class as that.Base and does not compile with the following error on gcc:

<source>:35:49: error: invalid use of 'Base::Base'
   35 |                                    : Base{ that.Base }
      |                                                 ^~~~
<source>:35:54: error: no matching function for call to 'Base::Base(<brace-enclosed initializer list>)'
   35 |                                    : Base{ that.Base }
      |