This introduces temporary helpers block_to_list and list_to_block.
The job of block_to_list(), at least, could be done by simply writing "&block->instrs" everywhere instead. Using the helper instead ensures that all of these instances will eventually be converted.
-- v2: vkd3d-shader/hlsl: Store the fields of struct parse_if_body as hlsl_block pointers. vkd3d-shader/hlsl: Store the "instrs" field of struct parse_initializer as a hlsl_block pointer.