[Doc] Move supported extension specs (#21120)
device_default_context impl:
https://github.com/intel/llvm/commit/d76350b010a4568d9198a4415e663db899eb6579
platform_device_index impl:
https://github.com/intel/llvm/commit/195f88072444d00e8e7914b8d97f0070cc5a26a1
