Avoid unnecessary use of stored_fields in our docs. (#57488)

Generally we don't advocate for using `stored_fields`, and we're interested in
eventually removing the need for this parameter. So it's best to avoid using
stored fields in our docs examples when it's not actually necessary.

Individual changes:
* Avoid using 'stored_fields' in our docs.
* When defining script fields in top-hits, de-emphasize stored fields.

docs/painless/painless-guide/painless-walkthrough.asciidoc

@@ -132,10 +132,6 @@ First, let's look at the source data for a player by submitting the following re
 ----------------------------------------------------------------
 GET hockey/_search
 {
-  "stored_fields": [
-    "_id",
-    "_source"
-  ],
   "query": {
     "term": {
       "_id": 1
@@ -189,7 +185,7 @@ Date fields are exposed as
 `ZonedDateTime`, so they support methods like `getYear`, `getDayOfWeek`
 or e.g. getting milliseconds since epoch with `getMillis`. To use these
 in a script, leave out the `get` prefix and continue with lowercasing the
-rest of the method name. For example, the following returns every hockey 
+rest of the method name. For example, the following returns every hockey
 player's birth year:
 
 [source,console]

docs/reference/scripting/fields.asciidoc

@@ -26,8 +26,10 @@ Depending on how many documents you have, this could mean millions or billions
 of executions: these scripts need to be fast!
 
 Field values can be accessed from a script using
-<<modules-scripting-doc-vals,doc-values>>, or
-<<modules-scripting-stored,stored fields or `_source` field>>, which are explained below.
+<<modules-scripting-doc-vals,doc-values>>,
+<<modules-scripting-source, the `_source` field>>, or
+<<modules-scripting-stored, stored fields>>,
+each of which is explained below.
 
 [[scripting-score]]
 [float]
@@ -137,32 +139,27 @@ access `text` fields from scripts.
 ===================================================
 
 [float]
-[[modules-scripting-stored]]
-=== Stored fields and `_source`
-
-_Stored fields_ -- fields explicitly marked as
-<<mapping-store,`"store": true`>> -- can be accessed using the
-`_fields['field_name'].value` or `_fields['field_name']` syntax.
+[[modules-scripting-source]]
+=== The document `_source`
 
-The document <<mapping-source-field,`_source`>>, which is really just a
-special stored field,  can be accessed using the `_source.field_name` syntax.
-The `_source` is loaded as a map-of-maps, so properties within object fields
-can be accessed as, for example, `_source.name.first`.
+The document <<mapping-source-field,`_source`>> can be accessed using the
+`_source.field_name` syntax. The `_source` is loaded as a map-of-maps, so
+properties within object fields can be accessed as, for example,
+`_source.name.first`.
 
 [IMPORTANT]
-.Prefer doc-values to stored fields
+.Prefer doc-values to _source
 =========================================================
 
-Stored fields (which includes the stored `_source` field) are much slower than
-doc-values.  They are  optimised for returning several fields per result,
-while doc values are optimised for accessing the value of a specific field in
-many documents.
+Accessing the `_source` field is much slower than using doc-values. The
+_source field is optimised for returning several fields per result, while doc
+values are optimised for accessing the value of a specific field in many
+documents.
 
-
-It makes sense to use `_source` or stored fields when generating a
-<<request-body-search-script-fields,script field>> for the top ten hits from a search
-result but, for other search and aggregation use cases, always prefer using
-doc values.
+It makes sense to use `_source` when generating a
+<<request-body-search-script-fields,script field>> for the top ten hits from a
+search result but, for other search and aggregation use cases, always prefer
+using doc values.
 =========================================================
 
 
@@ -174,50 +171,80 @@ PUT my_index
 {
   "mappings": {
     "properties": {
-      "title": { <1>
-        "type": "text"
-      },
       "first_name": {
-        "type": "text",
-        "store": true
+        "type": "text"
       },
       "last_name": {
-        "type": "text",
-        "store": true
+        "type": "text"
       }
     }
   }
 }
 
 PUT my_index/_doc/1?refresh
 {
-  "title": "Mr",
   "first_name": "Barry",
   "last_name": "White"
 }
 
 GET my_index/_search
 {
   "script_fields": {
-    "source": {
+    "full_name": {
       "script": {
         "lang": "painless",
-        "source": "params._source.title + ' ' + params._source.first_name + ' ' + params._source.last_name" <2>
+        "source": "params._source.first_name + ' ' + params._source.last_name"
+      }
+    }
+  }
+}
+-------------------------------
+
+[float]
+[[modules-scripting-stored]]
+=== Stored fields
+
+_Stored fields_ -- fields explicitly marked as
+<<mapping-store,`"store": true`>> in the mapping -- can be accessed using the
+`_fields['field_name'].value` or `_fields['field_name']` syntax:
+
+[source,console]
+-------------------------------
+PUT my_index
+{
+  "mappings": {
+    "properties": {
+      "full_name": {
+        "type": "text",
+        "store": true
+      },
+      "title": {
+        "type": "text",
+        "store": true
       }
-    },
-    "stored_fields": {
+    }
+  }
+}
+
+PUT my_index/_doc/1?refresh
+{
+  "full_name": "Alice Ball",
+  "title": "Professor"
+}
+
+GET my_index/_search
+{
+  "script_fields": {
+    "name_with_title": {
       "script": {
         "lang": "painless",
-        "source": "params._fields['first_name'].value + ' ' + params._fields['last_name'].value"
+        "source": "params._fields['title'].value + ' ' + params._fields['full_name'].value"
       }
     }
   }
 }
 -------------------------------
 
-<1> The `title` field is not stored and so cannot be used with the `_fields[]` syntax.
-<2> The `title` field can still be accessed from the `_source`.
-
 [TIP]
 .Stored vs `_source`
 =======================================================

docs/reference/search/request/highlighting.asciidoc

@@ -309,7 +309,6 @@ highlighting would only take the search query into account.
 --------------------------------------------------
 GET /_search
 {
-    "stored_fields": [ "_id" ],
     "query" : {
         "match": {
             "comment": {
@@ -331,6 +330,7 @@ GET /_search
             "rescore_query_weight" : 10
         }
     },
+    "_source": false,
     "highlight" : {
         "order" : "score",
         "fields" : {