Performance issue with long text lines

[HermanKirshin]

Describe the bug

BiDiAlgorithm.ProcessIsolatedRunSequences has O(n²) complexity, and in case of regular left-to-right european alphanumeric texts its calculations even do not affect anything.

To Reproduce

Add TextBlock
Set text to a very long line (i.e. 30kb)
Perform frequent measure (i.e. window resize) - there will be significant freezes

Expected behavior

No response

Avalonia version

11.2

OS

No response

Additional context

No response

[Gillibald]

We are already enumerating all codepoints here: https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Base/Media/TextFormatting/Unicode/BiDiData.cs#L93

So we can detect if there is any processing needed.

In general, TextBlock isn't meant to be used with very long text because there is no virtualization

This isn't a bug but a current limitation

[HermanKirshin]

@Gillibald perhaps, if I understood the code correctly, I can suggest the following easy fix, not as fast as detecting and disabling processing completely, but it at least in most cases reduces complexity from O(n²) to O(n). As far as I understand applying rule W2 makes sense only if there are arabic letters, so changing this condition to (hasEN && hasAL) will reduce freezing, if there is no arabic text in the long line. I tried it, textboxes with 30kb sometimes lag a bit, but at least they do not hang the app completely.