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).

docs/source/api/composer.rst

@@ -40,6 +40,7 @@ Helper Methods and Builders
 
 .. autoclass:: SfgFunctionSequencer
     :members:
+    :inherited-members:
 
 .. autoclass:: SfgNodeBuilder
     :members:
@@ -50,6 +51,12 @@ Helper Methods and Builders
 .. autoclass:: SfgSwitchBuilder
     :members:
 
+.. module:: pystencilssfg.composer.class_composer
+
+.. autoclass:: SfgMethodSequencer
+    :members:
+    :inherited-members:
+
 Context and Cursor
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