Date fields do not show the correct start day of the week for users locale in the Atlaskit editor

Issue Summary

As a user I expect that the date in text fields (description/environment) should show the correct start day of the week (e.g. Monday) for their locale when creating/viewing an issue.

Users are able to set the start day of the week in issue view and issue-create text fields by setting their language (locale) in their profile settings (https://jira.atlassian.com/browse/JRACLOUD-71611 and https://jira.atlassian.com/browse/JRACLOUD-79960).

Steps to Reproduce

1.  In your profile settings, set a language where the start day of the week is different from your current one (e.g. UK English should show Monday) (https://id.atlassian.com/manage-profile/account-preferences) under "Language & Region" -> "Language".
2. Open the issue-create modal and type "//" or "/date" in a text field (description or environment), and observe that the first day of the week is not correct.

Expected Results

First day of the week (e.g. Monday) should correspond to the users locale setting.

Actual Results

First day of the week is always "Sunday".

Workaround

• No known workaround