Support functions in named and unnamed namespaces

[operasfantom]

[korifey]

@operasfantom prease provide detailed description with Expected and Actual sections

[operasfantom]

Steps to reproduce

• Let's try to generate tests for function in C++ code

namespace N {
    void f() {
        
    }
}

Expected

1 test generated

Actual

0 tests generated, 1 error generated

/home/utbot/tmp/utbot-W14Q/cxx_lib/different_parameters_klee.cpp:16:1: error: use of undeclared identifier 'f'; did you mean 'N::f'?
f();
^
N::f
/home/utbot/UTBotCpp/integration-tests/cpp-example/cxx_lib/different_parameters.cpp:78:10: note: 'N::f' declared here
    void f() {
         ^
1 error generated.

[operasfantom]

Steps to reproduce

• Let's try to generate tests for function in C++ code

namespace {
    void f() {
        
    }
}

Expected

The sole generated test was run successfully

Actual

1 error generated while running generated test

/home/utbot/UTBotCpp/integration-tests/cpp-example/tests/cxx_lib/different_parameters_test.cpp:21:5: error: use of undeclared identifier 'f'
    f();
    ^
1 error generated.