Fix multi-level pointer type tokenization in stackalloc and variable declarations

[Copilot]

The grammar only matched single * for pointer types. Multi-level pointers (int**, int***) beyond the first level were incorrectly tokenized as arithmetic operators instead of type punctuation.

Changes

• array-creation-expression: Changed pointer suffix from (?:\s*\?\s*)? to (?:\s*\*\s*)* followed by (?:\s*\?\s*)? to support multiple pointer levels before nullable suffix
• local-variable-declaration: Changed (?:\s*[?*]\s*)? to separate pointer pattern (?:\s*\*\s*)* and nullable pattern (?:\s*\?\s*)?

Example

unsafe
{
    int* p = stackalloc int[10];      // Already worked
    int** pp = stackalloc int*[10];   // Now tokenizes all * correctly  
    int*** ppp = stackalloc int**[10]; // Now tokenizes all * correctly
}

All pointer asterisks now consistently receive punctuation.separator.asterisk.cs scope.

Original prompt

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This section details on the original issue you should resolve

<issue_title>stackalloc for pointer array declaration</issue_title>
<issue_description>## Details

What editor are you seeing the problem in? (e.g. Atom, Visual Studio Code, etc.)
vscode
What version of the editor are you using?
1.88.1
What color theme are you using?
dark plus

Repro

unsafe
{
    int* p = stackalloc int[10];
    int** pp = stackalloc int*[10];
    int*** ppp = stackalloc int**[10];
    int**** pppp = stackalloc int***[10];
}

Please provide a code example and (optionally) a screenshot demonstrating the problem.</issue_description>

<agent_instructions>From the example, it appears that pointer only support one level of indirection and additional * are not being classified properly.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes stackalloc for pointer array declaration #319

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