Add Stretch for ContentAlignment on SettingsCard

[zhuxb711]

Fixes

This PR extends ContentAlignment

PR Type

What kind of change does this PR introduce?

• New mode Stretch for settings card, which allows Content to use all available spaces and collapsed rest of UI elements

What is the current behavior?

• Supports only Left, Right, Vertical currently
• SettingsExpander.Items do not accept custom controls except SettingsCard by default because ItemContainerStyleSelector, even it supports, custom control still needs to simulate the paddings just like SettingsCard using Padding="58,8,44,8"

What is the new behavior?

• New behavior creates the SettingsCard filled with Content within SettingsExpander
• Provide a new way for developer to set custom layout/control under the SettingsExpander using SettingsCard

PR Checklist

Please check if your PR fulfills the following requirements:

• Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• Based off latest main branch of toolkit
• Tested code with current supported SDKs
• New component
  • Documentation has been added
  • Sample in sample app has been added
  • Analyzers are passing for documentation and samples
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (if applicable)
• Header has been added to all new source files
• Contains NO breaking changes

Other information

[zhuxb711]

@dotnet-policy-service agree