js-on-sx: logical assignment &&= ||= ??=

js-compound-update gains logical-assign operators:
- &&= → (if (js-to-boolean lhs) rhs lhs)
- ||= → (if (js-to-boolean lhs) lhs rhs)
- ??= → (if nullish? rhs lhs)

427/429 unit (+4), 148/148 slice unchanged.

lib/js/transpile.sx

@@ -506,6 +506,27 @@
       ((= op "/=") (list (js-sym "js-div") lhs-expr rhs-expr))
       ((= op "%=") (list (js-sym "js-mod") lhs-expr rhs-expr))
       ((= op "**=") (list (js-sym "js-pow") lhs-expr rhs-expr))
+      ((= op "&&=")
+        (list
+          (js-sym "if")
+          (list (js-sym "js-to-boolean") lhs-expr)
+          rhs-expr
+          lhs-expr))
+      ((= op "||=")
+        (list
+          (js-sym "if")
+          (list (js-sym "js-to-boolean") lhs-expr)
+          lhs-expr
+          rhs-expr))
+      ((= op "??=")
+        (list
+          (js-sym "if")
+          (list
+            (js-sym "or")
+            (list (js-sym "=") lhs-expr nil)
+            (list (js-sym "js-undefined?") lhs-expr))
+          rhs-expr
+          lhs-expr))
       (else (error (str "js-compound-update: unsupported op: " op))))))
 
 (define