Switch AutoCompleteBox to using StyledProperty

[robloo]

What does the pull request do?

Switches the AutoCompleteBox to using StyledProperty where possible.

What is the current behavior?

AutoCompleteBox has many DirectProperty that cannot be styled.

What is the updated/expected behavior with this PR?

• Switches the AutoCompleteBox to using StyledProperty where possible
• SearchText remains a read-only DirectProperty
• Also fixed a few typos in comments that were easy to search for

How was the solution implemented (if it's not obvious)?

Obvious

Checklist

• [ ] Added unit tests (if possible)?
• Added XML documentation to any related classes?
• [ ] Consider submitting a PR to https://github.com/AvaloniaUI/Documentation with user documentation

Breaking changes

Yes, StyledProperty instead of DirectProperty usage but functionality is largely expanded for app developers.

Obsoletions / Deprecations

None

Fixed issues

Part of #9944

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0032054-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0032204-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]