(core) Change datepicker in DateEditor to use moment format, show AltText in DateEditor

Summary:
- Rather than translate from moment format to that of bootstrap-datepicker, use
  the customization methods to format datepicker dates using moment directly.
- Fix issue with parseDate() when format includes tokens like Mo or Do
- Fix issue in parseDateTime() that could produce an off-by-one error in date
  depending on local timezone.
- When opening DateEditor, show AltText value if present.

- Add crossorigin=anonymous to scripts that were missing it (including
  bootstrap-datepicker), to ensure that errors from them are reported properly
  rather than as 'Script error.'

Test Plan:
Added test cases to parseDate() test for low-level fixes; added a
browser test for the fixed DateEditor behavior.

Reviewers: alexmojaki

Reviewed By: alexmojaki

Differential Revision: https://phab.getgrist.com/D3169

app/common/parseDate.ts

@@ -200,7 +200,9 @@ export function parseDateTime(dateTime: string, options: ParseOptions): number |
     return;
   }
 
-  const dateString = moment.unix(date).format("YYYY-MM-DD");
+  // date is a timestamp of midnight in UTC, so to get a formatted representation (for parsing
+  // together with time), take care to interpret it in UTC.
+  const dateString = moment.unix(date).utc().format("YYYY-MM-DD");
   dateTime = dateString + ' ' + parsedTime.time + tzOffset;
   const fullFormat = "YYYY-MM-DD HH:mm:ss" + (tzOffset ? 'Z' : '');
   return moment.tz(dateTime, fullFormat, true, timezone).valueOf() / 1000;
@@ -213,7 +215,7 @@ export function parseDateTime(dateTime: string, options: ParseOptions): number |
 // feature.
 function _getPartialFormat(input: string, format: string): string {
   // Define a regular expression to match contiguous non-separators.
-  const re = /Y+|M+|D+|[a-zA-Z0-9]+/g;
+  const re = /Y+|M+o?|D+o?|[a-zA-Z0-9]+/ig;
   // Count the number of meaningful parts in the input.
   const numInputParts = input.match(re)?.length || 0;