Ignore control characters on text input

[danipen]

When hitting the Escape key or other control keys, the _selection?.OnTextInput() method is executed, passing the string "\u001B" (ASCII 27 control char) to the HandleTextInput method.

This method matches every row because this comparison always returns true (see this .NET fiddle), causing that the selection is moved 1 row down every time the user hits the Escape key:

string escapeSequence = "\u001B"; // ESC - ASCII char 27
Console.WriteLine("something".ToUpper().StartsWith(escapeSequence));

True

This PR changes filters out control characters on method OnTextInput.

@grokys Question: Should Avalonia filter out these events in OnTextInput when the text contains control characters?

[danipen]

I opened an issue in dotnet/runtime#103116

[danipen]

I changed the implementation to use StringComparison.Ordinal as recommended here.

[danipen]

Revert the latest changes, it's not a good practice to ignore culture, so it's probably a better implementation to filter out control characters at the beginning.