Add RTL Card Level support to UWP Renderer

[beervoley]

Related Issue

This PR fixes #6506.

Description

Although the documentation states that RTL property is supported on card level, in UWP scenario it was not the case. RTL property was not utilized and I think it was simply overlooked when UWP renderer was introduced.

I've added RTL property to AdaptiveCard class and properly used it to assign FlowDirection to the Root FrameworkElement

Sample Card

{
  "type": "AdaptiveCard",
  "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
  "version": "1.5",
  "rtl": true,
  "body": [
    {
      "type": "TextBlock",
      "text": "هذه كتلة نص",
      "wrap": true
    },
    {
      "type": "TextBlock",
      "text": "זהו בלוק טקסט",
      "wrap": true
    },
    {
      "type": "TextBlock",
      "text": "This is a text block",
      "wrap": true
    },
    {
      "type": "ColumnSet",
      "horizontalAlignment": "Center",
      "columns": [
        {
          "type": "Column",
          "rtl": false,
          "items": [
            {
              "type": "TextBlock",
              "text": "هذه كتلة نص",
              "wrap": true
            }
          ]
        }
      ]
    }
  ]
}

How Verified

Manually.

Microsoft Reviewers: Open in CodeFlow

[beervoley]

@paulcam206 should I add a unit test for this scenario?

[paulcam206]

@paulcam206 should I add a unit test for this scenario?

yes please :)

[paulcam206]

code looks good -- just need unit tests 👍

[beervoley]

code looks good -- just need unit tests 👍

added some tests :)

[beervoley]

/azp run AdaptiveCards-iOS-CI

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[beervoley]

/azp run android-ci.yml

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[beervoley]

/azp run android-ci.yml

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[paulcam206]

/azp run AdaptiveCards-iOS-CI

protip: you can also retrigger a build from the Checks tab