[dart2wasm] Add dynamic module tests to dart2wasm test builders.

3 failing tests have been approved.

Change-Id: Ia38cbce99e739f2ce67d0d60236b3006635837ef
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/414163
Reviewed-by: Alexander Thomas <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: natebiggs

tools/bots/test_matrix.json

@@ -2749,6 +2749,17 @@
             "dartaotruntime"
           ]
         },
+        {
+          "name": "dart2wasm dynamic modules",
+          "script": "out/ReleaseX64/dart",
+          "testRunner": true,
+          "arguments": [
+            "pkg/dynamic_modules/test/runner/main.dart",
+            "-ndart2wasm-linux-${runtime}",
+            "-rdart2wasm",
+            "--verbose"
+          ]
+        },
         {
           "name": "dart2wasm tests",
           "arguments": [