ESQL - docs for to_date_nanos (#120124)

I forgot to link the ToDateNanos docs when I merged that function.
---------

Co-authored-by: elasticsearchmachine <[email protected]>
 Conflicts:
	docs/reference/esql/functions/description/to_date_nanos.asciidoc
	docs/reference/esql/functions/kibana/definition/to_date_nanos.json
	docs/reference/esql/functions/kibana/docs/to_date_nanos.md
	docs/reference/esql/functions/layout/to_date_nanos.asciidoc

Author: not-napoleon

docs/reference/esql/functions/type-conversion-functions.asciidoc

@@ -18,6 +18,7 @@
 * <<esql-to_cartesianshape>>
 * experimental:[] <<esql-to_dateperiod>>
 * <<esql-to_datetime>>
+* <<esql-to_date_nanos>>
 * <<esql-to_degrees>>
 * <<esql-to_double>>
 * <<esql-to_geopoint>>
@@ -37,6 +38,7 @@ include::layout/to_cartesianpoint.asciidoc[]
 include::layout/to_cartesianshape.asciidoc[]
 include::layout/to_dateperiod.asciidoc[]
 include::layout/to_datetime.asciidoc[]
+include::layout/to_date_nanos.asciidoc[]
 include::layout/to_degrees.asciidoc[]
 include::layout/to_double.asciidoc[]
 include::layout/to_geopoint.asciidoc[]

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/convert/ToDateNanos.java

@@ -63,9 +63,9 @@ public class ToDateNanos extends AbstractConvertFunction {
     @FunctionInfo(
         returnType = "date_nanos",
         description = "Converts an input to a nanosecond-resolution date value (aka date_nanos).",
-        note = "The range for date nanos is 1970-01-01T00:00:00.000000000Z to 2262-04-11T23:47:16.854775807Z.  Additionally, integers "
-            + "cannot be converted into date nanos, as the range of integer nanoseconds only covers about 2 seconds after epoch.",
-        preview = true
+        note = "The range for date nanos is 1970-01-01T00:00:00.000000000Z to 2262-04-11T23:47:16.854775807Z, attepting to convert"
+            + "values outside of that range will result in null with a warning..  Additionally, integers cannot be converted into date "
+            + "nanos, as the range of integer nanoseconds only covers about 2 seconds after epoch."
     )
     public ToDateNanos(
         Source source,