General: Introduce polyfills for str_ends_with() and str_starts_with() added in PHP 8.0.

PHP 8.0 introduced two new functions: `str_ends_with()` and `str_starts_with()`. These perform a case-sensitive check indicating if the string to search in (haystack) ends or begins with the given substring (needle).

These polyfills make these functios available for use in Core.

Ref:
* PHP RFC https://wiki.php.net/rfc/add_str_starts_with_and_ends_with_functions
* PHP manual `str_ends_with()` https://www.php.net/manual/en/function.str-ends-with.php
* PHP manual `str_starts_with()`  https://www.php.net/manual/en/function.str-starts-with.php

Props costdev, hellofromTonya, pbearne, pbiron.
Fixes #54377.

git-svn-id: https://develop.svn.wordpress.org/trunk@52040 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/compat.php

@@ -435,6 +435,49 @@ if ( ! function_exists( 'str_contains' ) ) {
 	}
 }
 
+if ( ! function_exists( 'str_starts_with' ) ) {
+	/**
+	 * Polyfill for `str_starts_with()` function added in PHP 8.0.
+	 *
+	 * Performs a case-sensitive check indicating if
+	 * the haystack begins with needle.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for in the `$haystack`.
+	 * @return bool True if `$haystack` starts with `$needle`, otherwise false.
+	 */
+	function str_starts_with( $haystack, $needle ) {
+		if ( '' === $needle ) {
+			return true;
+		}
+		return 0 === strpos( $haystack, $needle );
+	}
+}
+
+if ( ! function_exists( 'str_ends_with' ) ) {
+	/**
+	 * Polyfill for `str_ends_with()` function added in PHP 8.0.
+	 *
+	 * Performs a case-sensitive check indicating if
+	 * the haystack ends with needle.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param string $haystack The string to search in.
+	 * @param string $needle   The substring to search for in the `$haystack`.
+	 * @return bool True if `$haystack` ends with `$needle`, otherwise false.
+	 */
+	function str_ends_with( $haystack, $needle ) {
+		if ( '' === $haystack && '' !== $needle ) {
+			return false;
+		}
+		$len = strlen( $needle );
+		return 0 === substr_compare( $haystack, $needle, -$len, $len );
+	}
+}
+
 // IMAGETYPE_WEBP constant is only defined in PHP 7.1 or later.
 if ( ! defined( 'IMAGETYPE_WEBP' ) ) {
 	define( 'IMAGETYPE_WEBP', 18 );