Refactor wp_registration_url() to accept an optional redirect parameter

[nirajgiriXD]

Description

This PR adds an optional $redirect parameter to wp_registration_url(), enabling redirection after registration, similar to other WordPress URL functions. If a redirect URL is provided, it’s added as a redirect_to query argument.

Changes Made

Added $redirect Parameter:

• Allows specifying a redirect URL for post-registration navigation.
• Checks if $redirect is provided, and if so, adds it as a redirect_to query argument to the base registration URL.
• The function now filters the updated $register_url and includes the $redirect parameter in the filter hook, ensuring custom modifications to the registration URL also have access to this parameter.

Testing Instruction

• Check wp_registration_url() with and without a redirect parameter.
• Verify that the generated URL correctly includes the redirect_to parameter when specified.

Trac ticket: https://core.trac.wordpress.org/ticket/27632

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