improve completions keyword for function like body (microsoft#25824)

Author: Kingwl

src/services/completions.ts

@@ -2125,7 +2125,7 @@ namespace ts.Completions {
                 case KeywordCompletionFilters.ConstructorParameterKeywords:
                     return isParameterPropertyModifier(kind);
                 case KeywordCompletionFilters.FunctionLikeBodyKeywords:
-                    return !isClassMemberCompletionKeyword(kind);
+                    return isFunctionLikeBodyKeyword(kind);
                 case KeywordCompletionFilters.TypeKeywords:
                     return isTypeKeyword(kind);
                 default:
@@ -2151,6 +2151,10 @@ namespace ts.Completions {
         }
     }
 
+    function isFunctionLikeBodyKeyword(kind: SyntaxKind) {
+        return kind === SyntaxKind.AsyncKeyword || !isClassMemberCompletionKeyword(kind);
+    }
+
     function keywordForNode(node: Node): SyntaxKind {
         return isIdentifier(node) ? node.originalKeywordKind || SyntaxKind.Unknown : node.kind;
     }

tests/cases/fourslash/completionInFunctionLikeBody.ts

@@ -15,6 +15,7 @@
 
 
 goTo.marker("1");
+verify.completionListContains("async", "async", /*documentation*/ undefined, "keyword");
 verify.not.completionListContains("public", "public", /*documentation*/ undefined, "keyword");
 verify.not.completionListContains("private", "private", /*documentation*/ undefined, "keyword");
 verify.not.completionListContains("protected", "protected", /*documentation*/ undefined, "keyword");
@@ -26,6 +27,7 @@ verify.not.completionListContains("get", "get", /*documentation*/ undefined, "ke
 verify.not.completionListContains("set", "set", /*documentation*/ undefined, "keyword");
 
 goTo.marker("2");
+verify.completionListContains("async", "async", /*documentation*/ undefined, "keyword");
 verify.not.completionListContains("public", "public", /*documentation*/ undefined, "keyword");
 verify.not.completionListContains("private", "private", /*documentation*/ undefined, "keyword");
 verify.not.completionListContains("protected", "protected", /*documentation*/ undefined, "keyword");
@@ -41,3 +43,4 @@ verify.completionListContainsClassElementKeywords();
 
 goTo.marker("4");
 verify.completionListContainsClassElementKeywords();
+