Fixes#5022.
The streaming chunks from Anthropic seem to violate an assumption
that is implicit in the stream_chunk_builder implementation: that
only tool_calls OR function_calls OR content will appear in a
streamed response. The repro in #5022 shows that you can get
content followed by tool calls.
These changes properly handle these combinations by building
separate lists of each type of chunk (note that in theory a chunk
could appear in multiple lists, e.g. both delta.tool_calls and
delta.content being present on one chunk).
90dd60fa71