[mathml] Update CSS math-superscript-shift to match the specification

This feature was initially implemented in [1] [2]. After discussion with
the CSSWG, the property and values have been renamed [3]. This CL performs
the following changes:
- Rename math-superscript-shift to math-shift
- Rename value "display" and "inline" to "normal" and "compact"
- Add a MathML test to verify the effect of CSS math-shift
  (rather than just testing indirectly via UA style sheet rules).
- Sort math-style / math-shift alphabetically

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2144185
[2] https://chromium-review.googlesource.com/c/chromium/src/+/2277814
[3] w3c/csswg-drafts#5388

Bug: 6606
Change-Id: I1c7c7c12954261217cafffabffbe044c6659db9e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2421662
Reviewed-by: Rob Buis <[email protected]>
Reviewed-by: Rune Lillesveen <[email protected]>
Commit-Queue: Frédéric Wang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#809259}

mathml/presentation-markup/scripts/cramped-001.html

@@ -8,7 +8,7 @@
 <link rel="help" href="https://mathml-refresh.github.io/mathml-core/#radicals-msqrt-mroot">
 <link rel="help" href="https://mathml-refresh.github.io/mathml-core/#displaystyle-and-scriptlevel-in-scripts">
 <link rel="help" href="https://mathml-refresh.github.io/mathml-core/#user-agent-stylesheet">
-<meta name="assert" content="Verify default calculation of math-superscript-shift-style on MathML elements">
+<meta name="assert" content="Verify default calculation of math-shift on MathML elements">
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script src="/mathml/support/feature-detection.js"></script>
@@ -138,6 +138,14 @@
           assert_cramped("mmultiscripts-005", false, "post-superscript");
       }, "mmultiscripts");
 
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("css-001", false);
+          assert_cramped("css-002", true);
+          assert_cramped("css-003", true);
+          assert_cramped("css-004", false);
+      }, "element with specified CSS math-style");
+
       done();
   }
 </script>
@@ -588,5 +596,31 @@
       </mmultiscripts>
     </math>
   </p>
+  <p>
+    <math id="css-001" style="math-shift: normal">
+      <msup class="testedElement">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math id="css-002" style="math-shift: compact">
+      <msup class="testedElement">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math id="css-003" style="math-shift: normal">
+      <msup class="testedElement" style="math-shift: compact">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math id="css-004" style="math-shift: compact">
+      <msup class="testedElement" style="math-shift: normal">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+  </p>
 </body>
 </html>