A bit of code refactor

[heku]

What does the pull request do?

1 Move IsDirect = true into DirectPropertyBase
The line below should be better moved into the base class DirectPropertyBase instead of DirectProperty<TOwner, TValue>.

IsDirect = true;

2 Rename IDirectPropertyAccessor.Owner to OwnerType
The internal interface IDirectPropertyAccessor should reuse the exising property name in AvaloniaProperty, not introduce a new
duplicate one.

[maxkatz6]

Thank you, but unfortunately removing Owner property is a breaking change. Some app might have used this property.
In some cases we can justify breaking changes, but I not in this one.

[heku]

No problem, I made the change as it's an internal interface, I agree it might impact some apps even it's a non public interface.

[cla-avalonia]

• All contributors have signed the CLA.

[heku]

@cla-avalonia agree

[heku]

@maxkatz6 Hi, since we already introduced a break change to internal interface IDirectPropertyAccessor in PR https://github.com/AvaloniaUI/Avalonia/pull/15342/files#diff-665144eae92b5414e2672936b5ee880232eed13fc446f309685985ec6ca311ac. How about re-open this PR?

[maxkatz6]

@heku that's an internal interface though. Also, it wasn't backported.

[maxkatz6]

In general, we have API validation on the CI builds. So, it there was any unwanted breaking change, we would know (unless there is a bug in the validator).