Fix validity checking in calc() divide operations

https://crrev.com/c/5909795 relaxed a restriction in type checking on
divide operations in calc() expressions but went too far in doing so -
per css-values-4, we still need to validate that the right side is a
number. This CL introduces the needed check and adds a WPT to validate.

Fixed: 381913623
Change-Id: I08f23d832f9647beb6e067a24226496cb75bb971
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6071943
Reviewed-by: Rune Lillesveen <[email protected]>
Commit-Queue: Kevin Babbitt <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1392351}

css/css-values/calc-unit-analysis.html

@@ -66,7 +66,8 @@
                      "multiplication of number and length");
   assert_invalid_value("margin-left", "calc(2px * 1px)", // invalid calc expression
                        "multiplication of length and length");
-
+  assert_invalid_value("margin-left", "calc(20 / 0.75rem)", // invalid calc expression
+                       "division by non-number");
 }
 
 run();