function isCompletionListBlocker(contextToken) {
                var start = new Date().getTime();
                var result = isInStringOrRegularExpressionOrTemplateLiteral(contextToken) ||
                    isSolelyIdentifierDefinitionLocation(contextToken) ||
                    isDotOfNumericLiteral(contextToken) ||
                    isInJsxText(contextToken);
                log("getCompletionsAtPosition: isCompletionListBlocker: " + (new Date().getTime() - start));
                return result;
            }
Finds the first node that "embraces" the position, so that one may
accurately aggregate locals from the closest containing scope.