58764: Fix return type and improve regex safety in WP_Rewrite::using_index_permalinks()

[rohitgit2411]

Summary

This change fixes the return type consistency of WP_Rewrite::using_index_permalinks() and improves regex safety.

Changes included

• Casts the return value of preg_match() to bool to ensure the method always returns a boolean value as documented.
• Uses preg_quote() on $this->index to prevent potential regex issues when special characters are present.
• Aligns actual behavior with documented return type (bool), improving consistency and developer expectations.

Rationale

Currently, using_index_permalinks() returns the raw result of preg_match(), which can be 1, 0, or false. This does not match the documented return type of bool.

Additionally, the regex pattern is vulnerable to unexpected behavior if $this->index contains special regex characters. While unlikely in core usage, escaping it improves robustness and prevents edge-case false positives.

Testing

• Verified existing permalink behavior remains unchanged.

• Added/updated unit tests covering:

  • Standard permalink structure with /index.php/
  • Non-index permalink structure
  • Handling of special characters in $index

Trac ticket

https://core.trac.wordpress.org/ticket/58764

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This Pull Request is for code review only. Please keep all discussion in the Trac ticket. No merge action is required on GitHub.

[github-actions]

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[github-actions]

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