Offer correct completion when between a boolean JSX attr and the close tag

Fixes microsoft#4574

Author: RyanCavanaugh

src/services/services.ts

@@ -3549,6 +3549,9 @@ namespace ts {
                             if (parent && (parent.kind === SyntaxKind.JsxSelfClosingElement || parent.kind === SyntaxKind.JsxOpeningElement)) {
                                 return <JsxOpeningLikeElement>parent;
                             }
+                            else if (parent.kind === SyntaxKind.JsxAttribute) {
+                                return <JsxOpeningLikeElement>parent.parent;
+                            }
                             break;
 
                         // The context token is the closing } or " of an attribute, which means

tests/cases/fourslash/tsxCompletion8.ts

@@ -0,0 +1,19 @@
+/// <reference path='fourslash.ts' />
+
+//@Filename: file.tsx
+//// declare module JSX {
+////     interface Element { }
+////     interface IntrinsicElements {
+////         div: { ONE: string; TWO: number; }
+////     }
+//// }
+//// var x = <div /*1*/ autoComplete /*2*/ />;
+
+
+goTo.marker('1');
+verify.completionListContains("ONE");
+verify.not.completionListAllowsNewIdentifier();
+
+goTo.marker('2');
+verify.completionListContains("ONE");
+verify.not.completionListAllowsNewIdentifier();