Change the style of the Expander to respect the border properties

[skendrot]

Issue: #1583

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build or CI related changes
[ ] Documentation content changes
[ ] Sample app changes
[ ] Other... Please describe:

What is the current behavior?

Fixes issue where the Expander control does not respect the Border* properties

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added / updated (for bug fixes / features)
• Sample in sample app has been added / updated (for bug fixes / features)
• Tests for the changes have been added (for bug fixes / features) (if applicable)

What is the new behavior?

The Expander control will now honor the Border* properties

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This PR changes the Style of the Expander by replacing a Grid with a Border

[azchohfi]

Wow... talk about timing... I was reporting an issue that just got fixed by this PR. Changing the Background color of the Expander was changing the background color of the header even when it was expanded. This also fixed this bug. Thanks @skendrot.

[azchohfi]

Can you just pull the latest changes from master, just to double check that this does not conflict with the other PR that also changed the expander.

[azchohfi]

It was working, I double checked.