Expander fix for tab navigation, tab focus, and high contrast

[nmetulev]

Issue: #2276

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

• Tab order is broken (content focuses before header)
• User is able to focus inside overlay when it's not visible
• A border is visible in high contrast when it's not supposed to

What is the new behavior?

• Tab order works as expected
• User is no longer able to focus inside the overlay when it's not visible
• No border in high contrast mode

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Contains NO breaking changes

Other information

[windowstoolkitbot]

This PR is linked to unclosed issues. Please check if one of these issues should be closed: #2276