Explore: Support user timezone (#16469)

Explore now uses the timezone of the user to decide if local browser 
time or UTC should be used. 
- Now uses TimeRange instead of RawTimeRange in explore item
state tree and only parsing actual time in a few action
handlers.
- Time picker should now properly handle moving back/forward and
apply time range when both utc and non utc time zone.
- URL range representation is changed from YYYY-MM-DD HH:mm:ss
to epoch ms.
- Now uses AbsoluteTimeRange in graph component instead of moment.
- Makes a copy of the time range passed to timeSrv to make sure immutability
of explore time range when for example elasticsearch test datasources uses
timeSrv and sets a time range of last 1 min.
- Various refactorings and cleanup.

Closes #12812

packages/grafana-ui/src/types/time.ts

@@ -11,11 +11,30 @@ export interface TimeRange {
   raw: RawTimeRange;
 }
 
+export interface AbsoluteTimeRange {
+  from: number;
+  to: number;
+}
+
 export interface IntervalValues {
   interval: string; // 10s,5m
   intervalMs: number;
 }
 
+export interface TimeZone {
+  raw: string;
+  isUtc: boolean;
+}
+
+export const parseTimeZone = (raw: string): TimeZone => {
+  return {
+    raw,
+    isUtc: raw === 'utc',
+  };
+};
+
+export const DefaultTimeZone = parseTimeZone('browser');
+
 export interface TimeOption {
   from: string;
   to: string;