Normative: set compatDisplay only if notation is "compact"

Address #1031
This is necessary because
1. compatDisplay does not make sense if notation is not compact
2. costly to implement resolvedOptions() w/o in v8 since currently v8 depends on icu's skeleton to get the compactDisplay and there are no defined value for the case while notation is not compact

Author: FrankYFTang

spec/pluralrules.html

@@ -29,7 +29,8 @@ <h1>Intl.PluralRules ( [ _locales_ [ , _options_ ] ] )</h1>
         1. Let _notation_ be ? GetOption(_options_, *"notation"*, ~string~, « *"standard"*, *"scientific"*, *"engineering"*, *"compact"* », *"standard"*).
         1. Set _pluralRules_.[[Notation]] to _notation_.
         1. Let _compactDisplay_ be ? GetOption(_options_, *"compactDisplay"*, ~string~, « *"short"*, *"long"* », *"short"*).
-        1. Set _pluralRules_.[[CompactDisplay]] to _compactDisplay_.
+        1. If _notation_ is *"compact"*, then
+          1. Set _pluralRules_.[[CompactDisplay]] to _compactDisplay_.
         1. Perform ? SetNumberFormatDigitOptions(_pluralRules_, _options_, 0, 3, _notation_).
         1. Return _pluralRules_.
       </emu-alg>