Fix unnecessary 301 canonical redirect for query string encoding

[sanketio]

This PR fixes unnecessary 301 redirect triggered by redirect_canonical() when a query string contains a + (plus sign) instead of %20.

While both + and %20 are valid representations of a space in a query string, WordPress's redirect_canonical() logic uses rawurlencode_deep(), which strictly follows RFC 3986 (using %20). When comparing the requested URL to the canonical candidate, the mismatch in encoding triggers a redirect. This can lead to redirect loops, increased server load, and cache poisoning in environments with edge caching.

Changes

• Updated redirect_canonical() in wp-includes/canonical.php to normalize query string encoding before comparison.
• Implemented a check that treats + and %20 as equivalent within the query string portion of the URL.
• Ensures that if the only difference between the current URL and the redirect candidate is the space encoding, the redirect is suppressed.

Testing Instructions

• Set up a WordPress site with pretty permalinks enabled.
• Navigate to a URL with a plus sign in a query parameter, for example: example.com/?s=hello+world.
• Before Patch: Observe a 301 redirect to example.com/?s=hello%20world.
• After Patch: The page should load directly without a 301 redirect.
• Verify that search results and other query-dependent pages still function correctly.

Trac ticket

• https://core.trac.wordpress.org/ticket/64376

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