[ci-fix] De-flake SafeAreaPerEdgeValidation with keyboard waits (refs #37557) (#37742)

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Workflow artifact: ci-fix
Artifact kind: deflake
Refs: #37557
Target branch: main
Attempt: 1/10


## Attempt 1 of 10

Synchronize `SafeAreaPerEdgeValidation` with actual keyboard visibility
before validating keyboard-dependent safe-area layouts.

### Previous attempts (prior commits on this PR)

None.

This attempt differs by: this is the first attempt.

## Root cause

The latest `main` build 1563072 failed
`Issue28986.SafeAreaPerEdgeValidation` on run 0 because `ContentGrid`
remained at height 2789 after tapping the entry, then passed on built-in
retry run 1. The test immediately queried layout after the tap without
proving that Android had shown the keyboard.

Flake class: test-quality

## Why this was flaky

`Issue28986.SafeAreaPerEdgeValidation` retried its layout assertion but
had no synchronization point confirming that Android had completed the
keyboard transition. Depending on keyboard animation timing, the
assertion could poll the unchanged pre-keyboard layout; build 1563072
demonstrates the intermittent fail-then-pass behavior.

## De-flake

The test now asserts `WaitForKeyboardToShow()` before measuring the
keyboard-visible layout and `WaitForKeyboardToHide()` before validating
the restored layout. Every existing layout assertion remains unchanged.
No timeout was increased, no retry attribute was added, and no assertion
was weakened.

## Fix

Add the existing Appium keyboard-state waits at the two transition
boundaries so the test evaluates the same behavior in deterministic UI
states.

## What is unverified / where I need help

- The Android UI test could not be run because this runner has no device
rig.
- Please confirm the API 36 SafeAreaEdges leg consistently observes both
transitions.

## Validation

- Command: `not run because no Android device rig is available`
- Result: not run

## Evidence

- Original failing build:
https://dev.azure.com/dnceng-public/public/_build/results?buildId=1554582
- Latest verified-failing build:
https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563072

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Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

Author: github-actions[bot]

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28986.cs

@@ -177,6 +177,7 @@ public void SafeAreaPerEdgeValidation()
 
 		// Open Soft Input test entry
 		App.Tap("SoftInputTestEntry");
+		Assert.That(App.WaitForKeyboardToShow(), Is.True, "Keyboard should be visible before validating the resized safe area");
 
 		// With AdjustNothing mode, the window doesn't resize or pan
 		// The MainGrid gets bottom padding from SoftInput, so ContentGrid should shrink
@@ -187,6 +188,7 @@ public void SafeAreaPerEdgeValidation()
 		});
 
 		App.DismissKeyboard();
+		Assert.That(App.WaitForKeyboardToHide(), Is.True, "Keyboard should be hidden before validating the restored safe area");
 
 		App.RetryAssert(() =>
 		{