[UWP] Fix 11946 Entry Clear Button Visibility initial value not honored

[bmacombe]

Description of Change

Clear Button Visibility set before the control is loaded, in code or XAML wasn't being honored.

This change adds updating the visibility based on the ClearButtonVisible state during OnApplyTemplate since that is the first time the clear button could be removed.

Issues Resolved

• fixes [Bug] ClearButtonVisibility.Never does not take effect on UWP (2) #11946

API Changes

None

Platforms Affected

• Core/XAML (all platforms)
• iOS
• Android
• UWP

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

Open issue page 8836 and follow the instructions

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[bmacombe]

rebased to Target 4.8

[bmacombe]

I looked at the test failure, I don't think it's related.

Info: .NET Core SDK/runtime 2.2 and 3.0 are now End of Life(EOL) and have been removed from all hosted agents. If you're using these SDK/runtimes on hosted agents, kindly upgrade to newer versions which are not EOL, or else use UseDotNet task to install the required version.
[command]"C:\Program Files\dotnet\dotnet.exe" cake --target=cg-uwp-run-tests-ci --verbosity=diagnostic --UWP_TEST_LIBRARY=D:\a\r1\a/build/win_build/UITests/Xamarin.Forms.Core.Windows.UITests.dll
Could not execute because the specified command or file was not found.