Docs: add API docs for gpu.platform

Adds Python API documentations for gpu.platform module.

Ref D12222

doc/python_api/sphinx_doc_gen.py

@@ -254,6 +254,7 @@ else:
         "gpu.shader",
         "gpu.state",
         "gpu.texture",
+        "gpu.platform",
         "gpu_extras",
         "idprop.types",
         "mathutils",
@@ -2000,6 +2001,7 @@ def write_rst_importable_modules(basepath):
         "gpu.shader": "GPU Shader Utilities",
         "gpu.state": "GPU State Utilities",
         "gpu.texture": "GPU Texture Utilities",
+        "gpu.platform": "GPU Platform Utilities",
         "bmesh": "BMesh Module",
         "bmesh.ops": "BMesh Operators",
         "bmesh.types": "BMesh Types",