tests/functional2: add framework for lang tests

This creates a framework similar to the old lang.sh from functional.
Some notable changes:
- instead of having a .flags file, a test.toml can declare flags
- additionally the test.toml can also declare extra files and multiple
runners for the given input file.
- there won't be any old tests hanging around anymore which weren't
deleted properly in the installation
- all files for a single test are defined decleratively and there won't
be any residues

Tests can be placed within the functional2/lang folder
most migrations should be rather clean

Implements: #825

Change-Id: I5f9149903ec5b078008969a4ae77305417c11475

tests/functional2/testlib/utils.py

@@ -66,3 +66,23 @@ def get_functional2_files_with_testlib(
             additional_files,
         )
     )
+
+
+def get_functional2_lang_files(additional_files: FileDeclaration | None = None) -> FileDeclaration:
+    if additional_files is None:
+        additional_files = {}
+    return get_functional2_files_with_testlib(
+        merge_file_declaration(
+            {
+                "functional2": {
+                    "lang": {
+                        "__init__.py": CopyFile(functional2_base_folder / "lang/__init__.py"),
+                        "lang_util.py": CopyFile(functional2_base_folder / "lang/lang_util.py"),
+                        "test_lang.py": CopyFile(functional2_base_folder / "lang/test_lang.py"),
+                        "lib.nix": CopyFile(functional2_base_folder / "lang/lib.nix"),
+                    }
+                }
+            },
+            additional_files,
+        )
+    )