RTL Maldivian/Dhivehi (Thaana) text is not displayed correctly in WPF textboxes

* Windows version: (`winver`) Windows 10
* Does the bug reproduce also in WPF for .NET Framework 4.8?: Yes
* Is this bug related specifically to tooling in Visual Studio (e.g. XAML Designer, Code editing, etc...)? No
* Security issues and bugs should be reported privately, learn more via our [responsible disclosure guidelines](https://github.com/dotnet/wpf/blob/master/README.md#reporting-security-issues-and-security-bugs).

**Problem description:**
When inputting certain right-to-left language scripts in a WPF text box with an English OS, the characters are reversed.

Issue is reproducible with certain right-to-left languages, like Dhivehi/Thaana and Uyghur/Uighur Arabic, but not others like Hebrew and Arabic.

**Actual behavior:**
Reversed text (incorrect)

**Expected behavior:**
Correct Text:

**Minimal repro:**
1. In a simple WPF application, copy the text `ތާނަ` from [Wiki page](https://en.wikipedia.org/wiki/Thaana),
2. Observe that Thaana script is shown reversed