LibJS: Implement non standard error.stack attribute

All other browser already support this feature.
There is a Stage 1 proposal to standardize this, but it does not seem
to be active.

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -436,6 +436,7 @@ namespace JS {
     P(source)                                \
     P(splice)                                \
     P(sqrt)                                  \
+    P(stack)                                 \
     P(startOfDay)                            \
     P(startsWith)                            \
     P(status)                                \