Esql Support date nanos on date diff function (#120645)

Resolves #109999

This adds support for date nanos in the date diff function, as well as mixed nanos/millis use cases.

---------

Co-authored-by: elasticsearchmachine <[email protected]>

Author: not-napoleon

docs/changelog/120645.yaml

@@ -0,0 +1,6 @@
+pr: 120645
+summary: Esql Support date nanos on date diff function
+area: ES|QL
+type: enhancement
+issues:
+ - 109999

docs/reference/esql/functions/kibana/definition/date_diff.json

@@ -1249,3 +1249,28 @@ sv_nanos:date_nanos               | a:keyword             | b:keyword  | c:keywo
 2023-03-23T12:15:03.360103847Z | 2023-03-23T12:15:03.360Z | 2023-03-23 | 2023-03-23T12:15:03.360103847Z
 2023-03-23T12:15:03.360103847Z | 2023-03-23T12:15:03.360Z | 2023-03-23 | 2023-03-23T12:15:03.360103847Z
 ;
+
+Date Nanos Date Diff
+required_capability: date_nanos_date_diff
+required_capability: to_date_nanos
+
+FROM date_nanos
+| EVAL n = MV_MAX(nanos)
+| EVAL diff_sec = DATE_DIFF("seconds", TO_DATE_NANOS("2023-10-23T12:15:03.360103847Z"), n)
+| EVAL diff_sec_m = DATE_DIFF("seconds", TO_DATETIME("2023-10-23T12:15:03.360103847Z"), n)
+| KEEP diff_sec, diff_sec_m, n;
+ignoreOrder:true
+
+# Note - it is expected that the millisecond diff is slightly different due to rounding.
+diff_sec:integer | diff_sec_m:integer | n:date_nanos
+5998             | 5998             | 2023-10-23T13:55:01.543123456Z
+5932             | 5932             | 2023-10-23T13:53:55.832987654Z
+5871             | 5871             | 2023-10-23T13:52:55.015787878Z
+5811             | 5811             | 2023-10-23T13:51:54.732102837Z
+4711             | 4711             | 2023-10-23T13:33:34.937193000Z
+745              | 745              | 2023-10-23T12:27:28.948000000Z
+0                | 0                | 2023-10-23T12:15:03.360103847Z
+0                | 0                | 2023-10-23T12:15:03.360103847Z
+-18489600        | -18489599        | 2023-03-23T12:15:03.360103847Z
+-18489600        | -18489599        | 2023-03-23T12:15:03.360103847Z
+;