Extend Support for CUDA and HIP kernel invocations

This MR extends the support for CUDA and HIP kernel invocations and API reflection in pystencils-sfg, reflecting the concepts introduced in pystencils!449 (merged).

• Move GPU-related stuff into new composer mix-in SfgGpuComposer
• Replace cuda_invoke() by gpu_invoke()
• Implement three separate signatures of gpu_invoke(), depending on the kernel indexing scheme selected by the user
• Replace extensions.gpu by lang.gpu
• Add explanations on GPU kernels to user manual
• Fix some errors and clarify some interface descriptions in the user manual

This MR will already be using Target.HIP and therefore will have to wait for pystencils!458 (merged).

tests/generator_scripts/test_generator_scripts.py

@@ -24,7 +24,12 @@ PYSTENCILS_RT_INCLUDE_PATH = get_pystencils_include_path()
 TEST_INDEX = THIS_DIR / "index.yaml"
 SOURCE_DIR = THIS_DIR / "source"
 EXPECTED_DIR = THIS_DIR / "expected"
-CXX_INCLUDE_FLAGS = ["-I", f"{DEPS_DIR}/{MDSPAN_QUAL_PATH},{PYSTENCILS_RT_INCLUDE_PATH}"]
+CXX_INCLUDE_FLAGS = [
+    "-I",
+    f"{DEPS_DIR}/{MDSPAN_QUAL_PATH}",
+    "-I",
+    PYSTENCILS_RT_INCLUDE_PATH,
+]
 
 
 def prepare_deps():