[Feature Request] Positive lookbehind not working

Reproducible in vscode.dev or in VS Code Desktop?

• Not reproducible in vscode.dev or VS Code Desktop

Reproducible in the monaco editor playground?

• Not reproducible in the monaco editor playground

Monaco Editor Playground Code

monaco.editor.defineTheme('LuaTheme', {
    colors: {},
    base: 'vs',
    inherit: true,
    rules: [
        { token: 'attribute', foreground: 'ff0000', fontStyle: 'bold' }
        ]
});

monaco.languages.setMonarchTokensProvider('lua', {
    tokenizer: {
        root: [
            [/(?<=\.)[a-zA-Z0-9]+/, 'attribute']
        ]
   } 
})

monaco.editor.create(document.getElementById('container'), {
	language: 'lua',
    theme: 'LuaTheme'
});

Reproduction Steps

No response

Actual (Problematic) Behavior

When providing the input 'test.test.test' it does not match anything.

Expected Behavior

It should match the second and third 'test'.

Additional Context

I tried the positive lookahead, which is working fine.

Start with the Monaco Editor playground example and the monaco.languages.setMonarchTokensProvider entry point shown in the issue. Reproduce the test.test.test input with the provided Lua tokenizer and compare positive lookbehind with the working lookahead case. Done means the second and third test segments receive the expected token without breaking the existing tokenizer behavior.