Call InvalidateMeasure on DockLayout when properties change affecting layout

[BretJohnson]

Description of Change

When properties are updated affecting layout, InvalidateMeasure should be called to trigger the layout to happen, normally called via a propertyChanged notification. This PR adds that for DockLayout. The InvalidateMeasure method added here is similar to what's called for Grid properties in the MAUI repo.

Linked Issues

• Fixes [BUG] DockLayout doesn't update when DockPosition updated via Hot Reload / code behind #1250

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pull/XYZ

Additional information

Note that I attempted adding unit tests, but none of my attempts were able to catch the behavior difference when InvalidateMeasure is called. This may be something normally done by "device tests" in the MAUI repo. So I ended up just testing manually against my test repo, which all looked good.

[brminnick]

Thanks Bret!

Just curious - are there any severe performance impacts to this? In other words, should we wrap InvalidateMeasure in #if DEBUG so that it works in Hot Reload and avoids any potential performance problems?

[BretJohnson]

Thanks Bret!

Just curious - are there any severe performance impacts to this? In other words, should we wrap InvalidateMeasure in #if DEBUG so that it works in Hot Reload and avoids any potential performance problems?

No, doing the InvalidateMeasure when updating properties that can affect layout is expected - all the built in MAUI controls do it. Note that it's not only needed for Hot Reload; it's also needed when those properties are updated (beyond what's in the original XAML) by C# code. So it's a potential app runtime problem too, not just a Hot Reload issue.

[brminnick]

Thanks Bret!