This commit introduces a new execution mode for the
`simple_query_string` query, which is intended down the road to be a
replacement for the current _all field.
It now does auto-field-expansion and auto-leniency when the following criteria
are ALL met:
The _all field is disabled
No default_field has been set in the index settings
No fields are specified in the request
Additionally, a user can force the "all-like" execution by setting the
all_fields parameter to true.
When executing in all field mode, the `simple_query_string` query will
look at all the fields in the mapping that are not metafields and can be
searched, and automatically expand the list of fields that are going to
be queried.
Relates to #20925, which is the `query_string` version of this work.
This is basically the same behavior, but for the `simple_query_string`
query.
Relates to #19784
7420fd0be3