Add some redirects for sections that were renamed

This adds some redirects for header fragments that have changed to
help external links go to the correct location.

Author: ehuss

src/expressions/if-expr.md

@@ -186,3 +186,17 @@ r[expr.if.edition2024]
 [`match` expressions]: match-expr.md
 [boolean type]: ../types/boolean.md
 [scrutinee]: ../glossary.md#scrutinee
+
+<script>
+(function() {
+    var fragments = {
+        "#if-let-expressions": "if-expr.html#if-let-patterns",
+    };
+    var target = fragments[window.location.hash];
+    if (target) {
+        var url = window.location.toString();
+        var base = url.substring(0, url.lastIndexOf('/'));
+        window.location.replace(base + "/" + target);
+    }
+})();
+</script>

src/expressions/loop-expr.md

@@ -400,3 +400,17 @@ In the case a `loop` has an associated `break`, it is not considered diverging,
 [boolean type]: ../types/boolean.md
 [scrutinee]: ../glossary.md#scrutinee
 [temporary values]: ../expressions.md#temporaries
+
+<script>
+(function() {
+    var fragments = {
+        "#predicate-pattern-loops": "loop-expr.html#while-let-patterns",
+    };
+    var target = fragments[window.location.hash];
+    if (target) {
+        var url = window.location.toString();
+        var base = url.substring(0, url.lastIndexOf('/'));
+        window.location.replace(base + "/" + target);
+    }
+})();
+</script>