Subtracting 1-year from date during Reiwa 1 yields unexpected results.

[MicrosoftIssueBot]

Describe the bug
When using Japanese era globalization settings, adding/subtracting years can yield unexpected results.

Steps To Reproduce

1. Set your globalization settings to Japanese and use the Era notation for Calendar format
2. Open calculator and go to date calculation
3. Switch to add/subtract mode
4. Set the date to Reiwa 1-nen May 1
5. Subtract 1 year from that date
6. Note the result is Heisei 31-nen Apr 1

Expected behavior

the result should be Heisei 30, May 1
Screenshots

Device and Application Information

• OS Build: 17763
• Architecture: x64
• Application Version:
• Region:
• Dev Version Installed:

Additional context

The Japanese Era system can have multiple year partitions within the same year.
For example, April 30, 2019 is denoted April 30, Heisei 31; May 1, 2019 is denoted as May 1, Reiwa 1. The Calendar treats Heisei 31 and Reiwa 1 as separate years, which results in some unexpected behaviors where subtracting a year from Reiwa 1 results in a date in Heisei 31.

[MicrosoftIssueBot]

This is your friendly Microsoft Issue Bot. I created this issue automatically as requested by a team member.

[EriWong]

There is a further issue with how the calendar handles month boundaries. If a year transition happens in the middle of a month, the calendar treats the end of the month as a different month than the beginning of the month.