Update semantics

[rachelkang]

Description of Change

• Update semantics page to address differences between iOS and Android
• Make controls that have semantics also be screen reader accessible by default
• On Android: Use AccessibilityDelegate info.Text instead of contentDescription
• On Android: Make EditText description get read aloud, consistent with iOS and helpful for LabeledBy alternative

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)
• Targets a single property for a single control (or intertwined few properties)
• Adds the property to the appropriate interface
• Avoids any changes not essential to the handler property
• Adds the mapping to the PropertyMapper in the handler
• Adds the mapping method to the Android, iOS, and Standard aspects of the handler
• Implements the actual property updates (usually in extension methods in the Platform section of Core)
• Tags ported renderer methods with [PortHandler]
• Adds an example of the property to the sample project (MainPage)
• Adds the property to the stub class
• Implements basic property tests in DeviceTests

Does this PR touch anything that might affect accessibility?

• Does this PR introduce a new control? (If yes, add an example using SemanticProperties to the SemanticsPage)
• APIs that modify focusability?
• APIs that modify any text property on a control?
• Does this PR modify view nesting or view arrangement in anyway?
• Is there the smallest possibility that your PR will change accessibility?
• I'm not sure, please help me

If any of the above checkboxes apply to your PR, then the PR will need to provide testing to demonstrate that accessibility still works.

[PureWeen]

I wonder how these read on XCT?

Like if we use the AccessibilityDelegate instead of the content description

[rachelkang]

It reads the same on XCT at the moment

[PureWeen]

These should only get set if there's an actual value set for Description/Hint

[rachelkang]

fixing now - but can you remind me why the null check is sufficient for Android and not iOS?

[PureWeen]

That statement applies to both Android and iOS

[rachelkang]

gotcha - will fix both here and in XCT soon

[PureWeen]

Based on our conversations we need to fix Android to read out like iOS with the Entry control

[PureWeen]

Add a layout example so we can see the behaviors on a layout

<stacklayout SemanticProperty.Description="Hello">
<label
<button

<stacklayout SemanticProperty.Description="Hello">
<label
<label

[PureWeen]

Because we switched to using delegates for reading out the semantic description we can no longer verify these values through unit tests