Test @typedef in @typedef-only JS files

Previously there was nothing for the @typedef to attach to, so the
comment was never parsed. Now these comments attach to the EOF token.

Author: sandersn

tests/baselines/reference/jsdocTypeDefAtStartOfFile.symbols

@@ -0,0 +1,12 @@
+=== tests/cases/conformance/jsdoc/dtsEquivalent.js ===
+/** @typedef {{[k: string]: any}} AnyEffect */
+No type information for this code./** @typedef {number} Third */
+No type information for this code.=== tests/cases/conformance/jsdoc/index.js ===
+/** @type {AnyEffect} */
+let b;
+>b : Symbol(b, Decl(index.js, 1, 3))
+
+/** @type {Third} */
+let c;
+>c : Symbol(c, Decl(index.js, 3, 3))
+

tests/baselines/reference/jsdocTypeDefAtStartOfFile.types

@@ -0,0 +1,12 @@
+=== tests/cases/conformance/jsdoc/dtsEquivalent.js ===
+/** @typedef {{[k: string]: any}} AnyEffect */
+No type information for this code./** @typedef {number} Third */
+No type information for this code.=== tests/cases/conformance/jsdoc/index.js ===
+/** @type {AnyEffect} */
+let b;
+>b : { [k: string]: any; }
+
+/** @type {Third} */
+let c;
+>c : number
+

tests/cases/conformance/jsdoc/jsdocTypeDefAtStartOfFile.ts

@@ -0,0 +1,11 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @Filename: dtsEquivalent.js
+/** @typedef {{[k: string]: any}} AnyEffect */
+/** @typedef {number} Third */
+// @Filename: index.js
+/** @type {AnyEffect} */
+let b;
+/** @type {Third} */
+let c;