refactor: add initial language test fixtures for C, C++, Elixir and Java

tests/fixtures/languages/c/hello.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main() {
+    printf("Hello, World!\n");
+    return 0;
+}

tests/fixtures/languages/cpp/hello.cpp

@@ -0,0 +1,6 @@
+#include <iostream>
+
+int main() {
+    std::cout << "Hello, World!" << std::endl;
+    return 0;
+}

tests/fixtures/languages/elixir/greeter.ex

@@ -0,0 +1,5 @@
+defmodule Greeter do
+  def hello(name) do
+    IO.puts("Hello, #{name}!")
+  end
+end

tests/fixtures/languages/java/Test.java

@@ -0,0 +1,16 @@
+public interface Greeting {
+    String greet(String name);
+}
+
+public class Test implements Greeting {
+    private String prefix = "Hello";
+
+    public String greet(String name) {
+        return prefix + ", " + name + "!";
+    }
+
+    public static void main(String[] args) {
+        Test greeter = new Test();
+        System.out.println(greeter.greet("World"));
+    }
+}