Incorrect render of Thai characters when ascii characters are present in rendered text

[eangelov]

Prerequisites

• [x] I have written a descriptive issue title
• [x] I have verified that I am running the latest version of ImageSharp.Drawing
• [x] I have verified if the problem exist in both DEBUG and RELEASE mode
• [x] I have searched open and closed issues to ensure it has not already been reported

Description

When using DrawText on the test image to draw "ดวันโอวัน" everything is as expected

When we draw "Test ดวันโอวัน" we get

Test Image:

Steps to Reproduce

using SixLabors.Fonts;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Drawing.Processing;
using SixLabors.ImageSharp.Processing;

var fonts = new FontCollection();
fonts.AddSystemFonts();

string textToDraw = "ดวันโอวัน";

TextOptions textOpts = new TextOptions( fonts.Get( "Microsoft Sans Serif" ).CreateFont( 60, SixLabors.Fonts.FontStyle.Regular ) ){
    Origin = new SixLabors.ImageSharp.PointF( 10, 10 )
};

using Image image = Image.Load( "testImage.jpg" );
image.Mutate( 
    x => x.DrawText( 
        textOpts, textToDraw, Color.ParseHex( "#000000" ) 
    ) 
);
image.SaveAsJpeg( "resultImage_1.jpg" );

using Image image2 = Image.Load( "testImage.jpg" );
image2.Mutate( 
    x => x.DrawText( 
        textOpts, $"Test {textToDraw}", Color.ParseHex( "#000000" ) 
    ) 
);
image2.SaveAsJpeg( "resultImage_2.jpg" );

System Configuration

• ImageSharp.Drawing version: 1.0.0-beta15
• Other ImageSharp packages and versions: SixLabors.Fonts 1.0.0-beta18, SixLabors.ImageSharp 2.1.3
• Environment (Operating system, version and so on): Windows 11 Pro Version: 21H2 OS build: 22000.856
• .NET Framework version: .NET 6
• Additional information:

[JimBobSquarePants]

See https://github.com/SixLabors/Fonts/issues/215 we don't have a shaper for it yet.

I'll have a look at why it changes when mixed with English though as that's odd.