HSEARCH-3863 Apply suggestions from code review

Co-authored-by: Yoann Rodière <yoann@hibernate.org>

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/logging/impl/Log.java

@@ -716,13 +716,13 @@ SearchException customIndexSettingsErrorOnLoading(String filePath, @Cause Except
 	SearchException customIndexSettingsJsonSyntaxErrors(String filePath, @Cause Exception cause,
 			@Param EventContext context);
 
-	@Message(id = ID_OFFSET + 134, value = "Missing first on sort with ascending order is not supported.")
+	@Message(id = ID_OFFSET + 134, value = "Invalid use of 'missing().first()' for an ascending distance sort. Elasticsearch always assumes missing values have a distance of '+Infinity', and this behavior cannot be customized.")
 	SearchException missingFirstOnAscSortNotSupported(@Param EventContext context);
 
-	@Message(id = ID_OFFSET + 135, value = "Missing last on sort with descending order is not supported.")
+	@Message(id = ID_OFFSET + 135, value = "Invalid use of 'missing().first()' for a descending distance sort. Elasticsearch always assumes missing values have a distance of '+Infinity', and this behavior cannot be customized.")
 	SearchException missingLastOnDescSortNotSupported(@Param EventContext context);
 
-	@Message(id = ID_OFFSET + 136, value = "Missing as on sort is not supported with Elasticsearch backend.")
+	@Message(id = ID_OFFSET + 136, value = "Invalid use of 'missing().use(...)' for a distance sort. Elasticsearch always assumes missing values have a distance of '+Infinity', and this behavior cannot be customized.")
 	SearchException missingAsOnSortNotSupported(@Param EventContext context);
 
 }

documentation/src/main/asciidoc/reference/search-dsl-sort.asciidoc

@@ -373,10 +373,12 @@ include::{sourcedir}/org/hibernate/search/documentation/search/sort/SortDslIT.ja
 // Search 5 anchors backward compatibility
 [[_handling_missing_values]]
 
-In case of <<search-dsl-sort-field, sort by field values>>, the documents that do not have any value for a sort field
-will appear in the last position by default.
-In case of <<search-dsl-sort-distance, sort by distance to a point>>, the documents that do not have any value for a sort field
-will be treated as they were at plus infinite distance from the given point.
+By default:
+
+* For <<search-dsl-sort-field,sorts by field values>>, the documents that do not have any value for a sort field
+  will appear in the last position.
+* For <<search-dsl-sort-distance,sorts by distance to a point>>, the documents that do not have any value for a sort field
+  will be treated as they were at plus infinite distance from the given point.
 
 The behavior for missing values can be controlled explicitly through the `.missing()` option:
 
@@ -388,7 +390,7 @@ The behavior for missing values can be controlled explicitly through the `.missi
 ====
 All these options are supported in case of sort by field values or in case of sort by distance to a point
 using the Lucene backend.
-In case of sort by distance to a point using the Elasticsearch backend, due to the current Elasticsearch APIs,
+In case of sort by distance to a point using the Elasticsearch backend, due to limitations of the Elasticsearch APIs,
 only the following combinations are supported:
 
 * `.missing().first()` using a descending order.