Dashboards: Conserve timestamp on time range copy-paste across timezones (#109769)

* fix(timepicker): preserve UTC timestamp on copy-paste across timezones

* test: add UTC copy/paste timezone conversion test

* Update packages/grafana-ui/src/components/DateTimePickers/TimeRangePicker/TimeRangeContent.test.tsx

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Remove duplicate mockClipboard clear

* Extract utility functions for formatting and converting time ranges

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

packages/grafana-data/src/datetime/rangeutil.ts

@@ -505,3 +505,14 @@ export function relativeToTimeRange(relativeTimeRange: RelativeTimeRange, now: D
     raw: { from, to },
   };
 }
+
+/**
+ * @internal
+ * Returns a RawTimeRange that has been converted so that from and to are strings
+ */
+export function formatRawTimeRange(range: RawTimeRange): RawTimeRange {
+  return {
+    from: isDateTime(range.from) ? range.from.toISOString() : range.from,
+    to: isDateTime(range.to) ? range.to.toISOString() : range.to,
+  };
+}