fix prompt helper init (#11379)

...core/llama_index/core/indices/common/struct_store/base.py

...a-index-core/llama_index/core/indices/common_tree/base.py

llama-index-core/llama_index/core/indices/prompt_helper.py

llama-index-core/llama_index/core/indices/tree/inserter.py

...re/llama_index/core/indices/tree/select_leaf_retriever.py

...index-core/llama_index/core/response_synthesizers/base.py

...ex-core/llama_index/core/response_synthesizers/factory.py

...core/llama_index/core/response_synthesizers/generation.py

...dex-core/llama_index/core/response_synthesizers/refine.py

...lama_index/core/response_synthesizers/simple_summarize.py

.../llama_index/core/response_synthesizers/tree_summarize.py

llama-index-core/llama_index/core/settings.py