Merge branch 'safari-is-baNaNas' into 'master'

Fix Safari displaying NaN for selected due date

## What does this MR do?

1. Stops using `Date.parse` to parse selected due dates. 
2. Refactors DueDateSelectors to be more maintainable and readable

## Are there points in the code the reviewer needs to double check?

**To review the actual fix, look here:** https://gitlab.com/gitlab-org/gitlab-ce/commit/4ad43ac3a12902d7ea01dc09f8a361b01c21a0ee. It would be difficult to pick out from the overall diff. 

## Why was this MR needed?

In Safari, the due date selector was displaying 'NaN' when a date is selected, which was being returned by `Date.parse`. Because `Date.parse` is implemented differently across browsers it's generally recommended to favor implicit Date parsing with the `Date` constructor. For more background on this, [see MDN on Date.parse](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/parse).

Also, the code for DueDateSelector was pretty messy, and its logic was very tightly coupled, so I refactored it. None of the basic logic changed, I just broke it up into smaller pieces and made it more OO. 

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22984

See merge request !6797

1 files changed, 1 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9d28227f960..447b7ffdfdf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -118,6 +118,7 @@ Please view this file on the master branch, on stable branches it's out of date.
   - Grouped pipeline dropdown is a scrollable container
   - Cleanup Ci::ApplicationController. !6757 (Takuya Noguchi)
   - Fixes padding in all clipboard icons that have .btn class
+  - Fix due date being displayed as NaN in Safari
   - Fix a typo in doc/api/labels.md
   - API: all unknown routing will be handled with 404 Not Found
   - Add docs for request profiling